Add typing annotations to hub.py and _jit_internal.py (#42252)
Summary:
xref: https://github.com/pytorch/pytorch/wiki/Guide-for-adding-type-annotations-to-PyTorch
Pull Request resolved: https://github.com/pytorch/pytorch/pull/42252
Reviewed By: malfet
Differential Revision: D22916480
Pulled By: ezyang
fbshipit-source-id: 392ab805b0023640a3b5cdf600f70638b375f84f
