Batching rule for torch.pow, torch.result_type (#43515)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/43515
This PR adds a batching rule for torch.pow. This required adding a
batching rule for torch.result_type.
Test Plan: - added new tests: `pytest test/test_vmap.py -v`
Reviewed By: cpuhrsch
Differential Revision: D23302737
Pulled By: zou3519
fbshipit-source-id: 2cade358750f6cc3abf45f81f2394900600927cc
