Description

In order to better match the rest of the framework code base, this PR restructures the implementation of the Material Date Picker. The current code structure for the date pickers is:

material/pickers
├── calendar_date_picker.dart
├── calendar_date_range_picker.dart
├── date_picker_common.dart
├── date_picker_deprecated.dart
├── date_picker_dialog.dart
├── date_picker_header.dart
├── date_range_picker_dialog.dart
├── date_utils.dart
├── input_date_picker.dart
├── input_date_range_picker.dart
└── pickers.dart

I would like to combine several of these and move everything up to the top level material directory as follows:

In addition, we should add new test files for the top level components:

test/material/calendar_date_picker_test
test/material/input_date_picker_form_field_test.dart

This should bring the code structure for the Date Pickers to be more inline with the rest of the flutter framework, and thus easier for people to follow. This will also remove un-exported public symbols that were still technically available for people to use.

Related Issues

Fixes: #69939

Tests

I added the following tests:

test/material/calendar_date_picker_test
test/material/input_date_picker_form_field_test.dart

And moved others around.

Checklist

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• I read the [Contributor Guide] and followed the process outlined there for submitting PRs.
• I signed the [CLA].
• I read and followed the [Flutter Style Guide], including [Features we expect every widget to implement].
• I read the [Tree Hygiene] wiki page, which explains my responsibilities.
• I updated/added relevant documentation (doc comments with ///).
• All existing and new tests are passing.
• The analyzer (flutter analyze --flutter-repo) does not report any problems on my PR.
• I am willing to follow-up on review comments in a timely manner.

Breaking Change

Did any tests fail when you ran them?

• No, no existing tests failed, so this is not a breaking change.