[JIT] add dtype as type annotation (#39741)
Summary:
make torch.dtype resolve as type annotation
Pull Request resolved: https://github.com/pytorch/pytorch/pull/39741
Reviewed By: jamesr66a
Differential Revision: D21956469
Pulled By: eellison
fbshipit-source-id: 492acd7403fa827a2e2c87fd08d31450fcb3a45e
