OpInfo for `nn.functional.cross_entropy` (#63547)
Summary:
Reference: https://github.com/facebookresearch/functorch/issues/78 and https://github.com/pytorch/pytorch/issues/54261
TODOs:
* [ ] Investigate autograd failures.
* [ ] Clean up `test_nn.py` for `cross_entropy`.
cc: mruberry zou3519
cc albanD mruberry jbschlosser walterddr
Pull Request resolved: https://github.com/pytorch/pytorch/pull/63547
Reviewed By: mruberry
Differential Revision: D32062955
Pulled By: zou3519
fbshipit-source-id: 2a62a4c28af51fb71159df2e262d05039d549b7e
