[JIT] Add mypy type annotations for JIT (#43862)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/43862
Test Plan: Imported from OSS
Reviewed By: eellison
Differential Revision: D23491151
Pulled By: SplitInfinity
fbshipit-source-id: 88367b89896cf409bb9ac3db7490d6779efdc3a4
