OpInfo for `nn.functional.layer_norm` (#63276)
Summary:
Please see https://github.com/facebookresearch/functorch/issues/78 and https://github.com/pytorch/pytorch/issues/54261.
Note:
* This PR also adds a reference test inspired by existing tests in `test_nn.py`.
cc: mruberry zou3519
Pull Request resolved: https://github.com/pytorch/pytorch/pull/63276
Reviewed By: ejguan
Differential Revision: D30452483
Pulled By: zou3519
fbshipit-source-id: 2578d01ca34e031668a41bd284db60c31ae1fba8
