Fix CUDA named tensor `copy_` (#26829)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/26829
The TensorIterator loop for `copy_` uses operations that are currently
unsupported by named tensors. The solution is to wrap `copy_` in a
function that does the name propagation and ignore names when running
the implementation of `copy_`. There is no test case because I'm not
sure how to trigger the incorrect behavior, but there is definitely code
in CUDA copy that doesn't support named tensors (expand_as isn't
supported):
https://github.com/pytorch/pytorch/blob/aaf30cdf36839bc3f21b1622fb91ff3e2983e8ea/aten/src/ATen/native/cuda/Copy.cu#L141-L148
Test Plan: - [namedtensor ci]
Differential Revision: D17577310
Pulled By: zou3519
fbshipit-source-id: e11c52243800e1331fad738084304badcfd51ae2
