Add TypeVar defaults for Generator and AsyncGenerator

[JelleZijlstra]

Now that PEP 696 has landed, we should add defaults to the Generator and AsyncGenerator types for the send and return types.

cc @Gobot1234 @Daverball (python/typeshed#11867 (comment))

Linked PRs

• gh-118647: Add defaults to typing.Generator and typing.AsyncGenerator #118648

[Gobot1234]

#110212 seems related as well