[Class modifiers] package:meta implementation

[pq]

New class modifiers

This issue tracks the package:meta implementation of the new class modifiers feature.

• implement @reopen #50977

Specs

• Sealed types
• Base-interface-final
• Type modifiers

[pq]

@kallentu, @munificent: besides @reopen, is there anything to do in annotation-land? (See: package:meta.)

[FMorschel]

"Type modifiers" is missing in master, at least, where are the specs? The other two have been moved but GitHub could find the files.

[pq]

Yeah. It looks like things have moved...

Here's a good place to start: https://github.com/dart-lang/language/blob/master/accepted/future-releases/class-modifiers/feature-specification.md

[pq]

Closing as @reopen has landed. (Support in the linter is tracked in #58976)