mypy

96366d1d - Don't ask to install a stub package if stubs are installed (#10670)

Don't ask to install a stub package if stubs are installed (#10670) If we encounter an import of a submodule of a package with installed stubs, and the submodule doesn't exist, don't ask to install stubs since that's not going to help. Also make it possible to ignore this error using `--ignore-missing-imports`. Work on #10645.