Support torch.pow with named tensors (#26541)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/26541
`torch.pow` already supports named tensors; every one of its constituent
codepaths propagates names:
- TensorIterator propagates names
- resize_as_ and fill_ propagate names (exponent == 0 or base == 1)
- resize_as_ and copy_ propagate names (exponent == 1)
This PR adds `supports_named_tensor = True` to the pow overloads,
enabling `pow` to take named tensors.
Test Plan: - [namedtensor ci]
Differential Revision: D17501402
Pulled By: zou3519
fbshipit-source-id: 07ee91d685e55dd58bbbb3a3fc9e185de8bb7515
