Describe the bug
When importing libraries, there is a check if this library actually exists dart(uri_does_not_exist). This is not called on conditional imports, such as

import 'something.dart' if(dart.library.js) import 'somethingelse.dart'

To Reproduce
Write

import 'something.dart' if(dart.library.js) import 'somethingelse.dart'

where 'something.dart' exists, but 'somethingelse.dart' doesn't.

Expected behavior
Should trigger on both.

Screenshots

Please complete the following information:

• Operating System and version: Linux
• VS Code version: 1.76.2
• Dart extension version: v3.63.20230502
• Dart/Flutter SDK version: Dart SDK version: 3.1.0-39.0.dev (dev) (Mon Apr 24 18:53:55 2023 -0700) on "linux_x64"