Add deprecation messages for functorch.* function transforms (#92279)
This PR:
- adds deprecation warnings when calling the functorch APIs
- adds documentation saying that those APIs are deprecated
It does this by creating thin wrappers around the original APIs that (1)
raise deprecation warnings and (2) have an additional line in their
documentation that they are deprecated.
NB:
- Python surpresses DeprecationWarning, so we use UserWarning instead.
Test Plan:
- New tests
- the functorch.* APIs are still tested for correctness because that's
what test/functorch/* use (as opposed to directly calling the
torch.func.* APIs)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/92279
Approved by: https://github.com/albanD, https://github.com/soulitzer
