Run mypy on some test files, add iinfo/finfo annotations (#38220)
Summary:
Most test files have a ton of errors; there's not much point adding ignores for them though. The way of working is simply to run `mypy test/test_somefile.py`, fix up the errors, then add that file to the `files =` list in `mypy.ini`.
Can't add all of `test/*` by default, because the JIT test files have (on purpose) syntax errors that are meant to exercise the robustness of the JIT to bad annotations. Leave those alone for now.
_Depends on the ghstacked PRs in gh-38173, only the last 2 commits are new._
Pull Request resolved: https://github.com/pytorch/pytorch/pull/38220
Differential Revision: D21503481
Pulled By: ezyang
fbshipit-source-id: 63026e73201c549d64647a03a20a4c6687720244
