Add support for class annotations (#21379)
Summary:
This adds support for inferred attributes (everything except empty lists, dicts, and tuples) as well as using the PEP 526 style annotations on a class, so this eliminates the need for `torch.jit.Attribute`
Pull Request resolved: https://github.com/pytorch/pytorch/pull/21379
Differential Revision: D15718537
Pulled By: driazati
fbshipit-source-id: b7481ae3d7ee421613e931b7dc3427ef2a99757f
