All supertypes of classes marked as "dyn-module:extendable" are technically also extendable in dynamic modules since subtyping is transitive.
Also skip marking 'final' classes as dynamic module extendable.
Change-Id: I124eae56b78b98aba8712158fda87bbc8e652ed3
Tested: Ran tests for dynamic interface annotator.
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/403960
Commit-Queue: Nate Biggs <natebiggs@google.com>
Reviewed-by: Alexander Markov <alexmarkov@google.com>
Nate Biggs