FLUTTER:OUTLINE is not shown for files from included packages & flutter core files. #5045

Describe the bug
Flutter:Outline is available for dart files in my project but not for dart files in included libraries. See attachment.

To Reproduce
Steps to reproduce the behavior:

1. Create a new flutter project.
2. Open in VS Code.
3. Open a dart file in the project and see flutter outline.
4. Open a dart file from flutter core and see flutter outline.

Expected behavior
Flutter outline should be shown for both the files.

Screenshots

Please complete the following information:

You can run the Dart: Collect Diagnostic Information command from the VS Code command palette (F1) to easily capture this information or provide it manually.

• Operating System and version: macos / Version 14.1 (Build 23B74)
• VS Code version: mac 1.87.2
• Dart extension version: 3.84.0
• Dart/Flutter SDK version:
  Dart (3.1.5): /Users/vaibhav/fvm/versions/3.13.9/bin/cache/dart-sdk
  Flutter (3.13.9): /Users/vaibhav/fvm/versions/3.13.9 (My Iphone 12 (ios/ios))
• Target device (if the issue relates to Flutter debugging):