Add basic support for Dart 3 features

[parlough]

Adds support for keywords from following features (with links to their feature specifications):

• The when keyword from patterns
• The declaration keywords:
  • base and interface from class modifiers
  • sealed from sealed types
  • inline from inline classes
• The Record type from records

Also removes the old interface from the :class declarations, since interface never existed in that form, it is instead a declaration modifier, similar to abstract.

[tancnle]

Thank you for your contribution @parlough. The PR looks good to me 🚀