Warn that annotations could be if TYPE_CHECKING

[jonfitt]

Would it be possible to get mypy to list all imports that are only used for annotations that are not in an if TYPE_CHECKING check?

It would be very useful to cleanup imports and head off potential circular import issues coming from annotation imports.

[brianschubert]

FWIW, this feature is currently provided by ruff's TCH rules / flake8-type-checking