[JIT] Update docs for recently added features (#45232)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/45232
**Summary**
This commit updates the TorchScript language reference to include
documentation on recently-added TorchScript enums. It also removed
`torch.no_grad` from the list of known unsupported `torch` modules and
classes because it is now supported.
**Test Plan**
Continuous integration.
Test Plan: Imported from OSS
Reviewed By: ZolotukhinM
Differential Revision: D23971884
Pulled By: SplitInfinity
fbshipit-source-id: 5e2c164ed59bc0926b11201106952cff86e9356e
