Unexpected behaviour of SliverAppBar in NestedScrollView on Mouse Scroll

I'm attempting to build a webpage using `NestedScrollView`. But I'm encountering various issues when scrolling by mouse wheel:
- SliverAppBar instantly collapses (`pinned: true`) or disappears (`floating: true`) on single mouse scroll tick.
- `floating: true` does not "float" the SliverAppBar, even after setting `snap: true`, unlike #17518.
- Keeping SliverOverlapAbsorber/SliverOverlapInjector never collapses SliverAppBar when `pinned` and `floating` are both set to `true` (Removing it fixes this issue).

Except for the last issue and #17518, the above-mentioned issues are not exhibited when mouse hold-and-drag is used to scroll the NestedScrollView.

## Steps to Reproduce



1. Run `flutter create bug`.
2. Update **main.dart** as follows: ... 
```dart
import 'dart:math' as math;

import 'package:flutter/material.dart';

var rnd = math.Random(602);

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
        visualDensity: VisualDensity.adaptivePlatformDensity,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: NestedScrollView(
        headerSliverBuilder: (context, isInnerBoxScrolled) {
          return [
            SliverOverlapAbsorber(
              handle: NestedScrollView.sliverOverlapAbsorberHandleFor(context),
              sliver: SliverAppBar(
                pinned: true,
                // floating: true,
                // snap: true,
                expandedHeight: 500.0,
                flexibleSpace: FlexibleSpaceBar(
                  title: Text(widget.title),
                ),
              ),
            ),
          ];
        },
        body: Builder(
          builder: (context) {
            return CustomScrollView(
              slivers: [
                SliverOverlapInjector(
                  handle:
                      NestedScrollView.sliverOverlapAbsorberHandleFor(context),
                ),
                SliverFixedExtentList(
                  delegate: SliverChildBuilderDelegate(
                    (context, index) {
                      return Container(
                        color: Colors
                            .primaries[rnd.nextInt(Colors.primaries.length)],
                        alignment: Alignment.center,
                        child: Text('Element $index'),
                      );
                    },
                    childCount: 40,
                  ),
                  itemExtent: 200.0,
                ),
              ],
            );
          },
        ),
      ),
    );
  }
}

```

<details>
  <summary>Logs</summary>



```
[  +25 ms] executing: [/home/anurag/flutter_master/] git -c log.showSignature=false log -n 1 --pretty=format:%H
[  +80 ms] Exit code 0 from: git -c log.showSignature=false log -n 1 --pretty=format:%H
[        ] f35b673f2b7ea7800c97d9ec096153fcca6091f2
[   +1 ms] executing: [/home/anurag/flutter_master/] git describe --match *.*.* --first-parent --long --tags
[  +35 ms] Exit code 0 from: git describe --match *.*.* --first-parent --long --tags
[        ] 1.18.0-dev.5.0-82-gf35b673f2
[  +33 ms] executing: [/home/anurag/flutter_master/] git rev-parse --abbrev-ref --symbolic @{u}
[  +12 ms] Exit code 0 from: git rev-parse --abbrev-ref --symbolic @{u}
[        ] origin/master
[        ] executing: [/home/anurag/flutter_master/] git ls-remote --get-url origin
[  +13 ms] Exit code 0 from: git ls-remote --get-url origin
[        ] https://github.com/flutter/flutter.git
[ +122 ms] executing: [/home/anurag/flutter_master/] git rev-parse --abbrev-ref HEAD
[  +17 ms] Exit code 0 from: git rev-parse --abbrev-ref HEAD
[        ] master
[ +156 ms] Artifact Instance of 'AndroidMavenArtifacts' is not required, skipping update.
[        ] Artifact Instance of 'AndroidGenSnapshotArtifacts' is not required, skipping update.
[        ] Artifact Instance of 'AndroidInternalBuildArtifacts' is not required, skipping update.
[        ] Artifact Instance of 'IOSEngineArtifacts' is not required, skipping update.
[        ] Artifact Instance of 'FlutterWebSdk' is not required, skipping update.
[   +8 ms] Artifact Instance of 'WindowsEngineArtifacts' is not required, skipping update.
[        ] Artifact Instance of 'MacOSEngineArtifacts' is not required, skipping update.
[        ] Artifact Instance of 'LinuxEngineArtifacts' is not required, skipping update.
[        ] Artifact Instance of 'LinuxFuchsiaSDKArtifacts' is not required, skipping update.
[        ] Artifact Instance of 'MacOSFuchsiaSDKArtifacts' is not required, skipping update.
[        ] Artifact Instance of 'FlutterRunnerSDKArtifacts' is not required, skipping update.
[        ] Artifact Instance of 'FlutterRunnerDebugSymbols' is not required, skipping update.
[  +44 ms] executing: /home/anurag/Android/Sdk/platform-tools/adb devices -l
[ +154 ms] List of devices attached
                    192.168.31.70:5555     device product:aosp_tissot model:Mi_A1 device:tissot transport_id:1
[  +19 ms] Artifact Instance of 'AndroidMavenArtifacts' is not required, skipping update.
[        ] Artifact Instance of 'AndroidGenSnapshotArtifacts' is not required, skipping update.
[        ] Artifact Instance of 'AndroidInternalBuildArtifacts' is not required, skipping update.
[        ] Artifact Instance of 'IOSEngineArtifacts' is not required, skipping update.
[   +6 ms] Artifact Instance of 'WindowsEngineArtifacts' is not required, skipping update.
[        ] Artifact Instance of 'MacOSEngineArtifacts' is not required, skipping update.
[        ] Artifact Instance of 'LinuxEngineArtifacts' is not required, skipping update.
[        ] Artifact Instance of 'LinuxFuchsiaSDKArtifacts' is not required, skipping update.
[        ] Artifact Instance of 'MacOSFuchsiaSDKArtifacts' is not required, skipping update.
[        ] Artifact Instance of 'FlutterRunnerSDKArtifacts' is not required, skipping update.
[        ] Artifact Instance of 'FlutterRunnerDebugSymbols' is not required, skipping update.
[ +504 ms] Generating
/media/D/AndroidStudioProjects/snap_on_scroll/android/app/src/main/java/io/flutter/plugins/GeneratedPluginRegistran
t.java
[ +328 ms] Launching lib/main.dart on Chrome in debug mode...
[ +201 ms] Updating assets
[ +210 ms] Syncing files to device Chrome...
[ +141 ms] Generating
/media/D/AndroidStudioProjects/snap_on_scroll/android/app/src/main/java/io/flutter/plugins/GeneratedPluginRegistran
t.java
[ +105 ms] <- reset
[  +20 ms] /home/anurag/flutter_master/bin/cache/dart-sdk/bin/dart
/home/anurag/flutter_master/bin/cache/artifacts/engine/linux-x64/frontend_server.dart.snapshot --sdk-root
/home/anurag/flutter_master/bin/cache/flutter_web_sdk/ --incremental --target=dartdevc --debugger-module-names
-Ddart.developer.causal_async_stacks=true --output-dill /tmp/flutter_tool.RSGRGE/app.dill --libraries-spec
file:///home/anurag/flutter_master/bin/cache/flutter_web_sdk/libraries.json --packages
/media/D/AndroidStudioProjects/snap_on_scroll/.packages -Ddart.vm.profile=false -Ddart.vm.product=false
--bytecode-options=source-positions,local-var-info,debugger-stops,instance-field-initializers,keep-unreachable-code
,avoid-closure-call-instructions --enable-asserts --track-widget-creation --filesystem-root
/tmp/flutter_tools.REABWD --filesystem-scheme org-dartlang-app --initialize-from-dill build/cache.dill --platform
file:///home/anurag/flutter_master/bin/cache/flutter_web_sdk/kernel/flutter_ddc_sdk.dill
[  +19 ms] <- compile org-dartlang-app:///web_entrypoint.dart
[+27336 ms] Syncing files to device Chrome... (completed in 27,602ms, longer than expected)
[   +2 ms] Synced 21.6MB.
[   +1 ms] <- accept
[ +508 ms] [CHROME]:
[   +1 ms] [CHROME]:DevTools listening on
ws://127.0.0.1:38443/devtools/browser/80ca58d1-ecf2-4800-ab22-6679a6d28d3d
[+5565 ms] Debug service listening on ws://127.0.0.1:42357/YvfFBa7bUgE=

[+1537 ms] Debug service listening on ws://127.0.0.1:42357/YvfFBa7bUgE=
[   +3 ms] Warning: Flutter's support for web development is not stable yet and hasn't
[        ] been thoroughly tested in production environments.
[        ] For more information see https://flutter.dev/web
[   +3 ms] 🔥  To hot restart changes while running, press "r". To hot restart (and refresh the browser), press
"R".
[   +3 ms] For a more detailed help message, press "h". To quit, press "q".

```





```
[✓] Flutter (Channel master, v1.18.0-6.0.pre.82, on Linux, locale en_US.UTF-8)
    • Flutter version 1.18.0-6.0.pre.82 at /home/anurag/flutter_master
    • Framework revision f35b673f2b (3 days ago), 2020-04-19 02:45:01 +0530
    • Engine revision a5e0b2f2f2
    • Dart version 2.9.0 (build 2.9.0-1.0.dev 5b19445d9c)

 
[✓] Android toolchain - develop for Android devices (Android SDK version 29.0.3)
    • Android SDK at /home/anurag/Android/Sdk
    • Platform android-29, build-tools 29.0.3
    • ANDROID_HOME = /home/anurag/Android/Sdk
    • Java binary at: /snap/android-studio/88/android-studio/jre/bin/java
    • Java version OpenJDK Runtime Environment (build 1.8.0_212-release-1586-b4-5784211)
    • All Android licenses accepted.

[✓] Chrome - develop for the web
    • CHROME_EXECUTABLE = /opt/brave.com/brave/brave

[✓] Linux toolchain - develop for Linux desktop
    • clang++ 6.0.0
    • GNU Make 4.1

[✓] Android Studio (version 3.6)
    • Android Studio at /snap/android-studio/88/android-studio
    • Flutter plugin version 45.1.1
    • Dart plugin version 192.7761
    • Java version OpenJDK Runtime Environment (build 1.8.0_212-release-1586-b4-5784211)

 
[✓] Connected device (4 available)            
    • Mi A1      • 192.168.31.70:5555 • android-arm64  • Android 10 (API 29)
    • Linux      • Linux              • linux-x64      • Linux
    • Chrome     • chrome             • web-javascript • Brave Browser 81.1.7.98 unknown
    • Web Server • web-server         • web-javascript • Flutter Tools

• No issues found!
```

</details>

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Unexpected behaviour of SliverAppBar in NestedScrollView on Mouse Scroll #55362

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Unexpected behaviour of SliverAppBar in NestedScrollView on Mouse Scroll #55362

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