Describe the bug
When using flutter_localizations, the extension doesn't lint/track AppLocalizations nor its import 'package:flutter_gen/gen_l10n/app_localizations.dart' automatically.

To Reproduce
Steps to reproduce the behavior:

1. Install and setup flutter_localizations
2. Go in any dart file and try to type AppLocalizations: no Quick Fix available, and we have to import the package manually.

Expected behavior
It should suggest import 'package:flutter_gen/gen_l10n/app_localizations.dart' in the Quick Fixes dropdown list.

Screenshots

Please complete the following information:

• Operating System and version: Windows 10.0.19044.1645
• VS Code version: 1.66.2
• Dart extension version: 3.40.0
• Dart/Flutter SDK version: Channel stable, 2.10.4
• Target device (if the issue relates to Flutter debugging): None