Address JIT/Mypy issue with torch._VF (#43454)
Summary:
- `torch._VF` is a hack to work around the lack of support for `torch.functional` in the JIT
- that hack hides `torch._VF` functions from Mypy
- could be worked around by re-introducing a stub file for `torch.functional`, but that's undesirable
- so instead try to make both happy at the same time: the type ignore comments are needed for Mypy, and don't seem to affect the JIT after excluding them from the `get_type_line()` logic
Encountered this issue while trying to make `mypy` run on `torch/functional.py` in gh-43446.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/43454
Reviewed By: glaringlee
Differential Revision: D23305579
Pulled By: malfet
fbshipit-source-id: 50e490693c1e53054927b57fd9acc7dca57e88ca
