Support for type annotations instead of torch.jit.annotate() (#21390)
Summary:
This adds support for PEP 526 style annotations on assignments in place of
`torch.jit.annotate()`, so
```python
a = torch.jit.annotate(List[int], [])
```
turns into
```python
a : List[int] = []
```
](https://our.intern.facebook.com/intern/diff/15706021/)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/21390
Pulled By: driazati
Differential Revision: D15706021
fbshipit-source-id: 8bf1459f229d5fd0e16e59953b9656e85a2207fb
