Batched grad support for: slice, select, diagonal (#44505)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/44505
Added batching rules for slice_backward, select_backward, and
diagonal_backward.
Test Plan: - new tests: `pytest test/test_vmap.y -v -k "BatchedGrad"`
Reviewed By: agolynski, anjali411
Differential Revision: D23650409
Pulled By: zou3519
fbshipit-source-id: e317609d068c88ee7bc07fab88b2b3acb8fad7e1
