Disables unary op casting to output dtype (#41097)
Summary:
Fixes https://github.com/pytorch/pytorch/issues/41047.
Some CPU kernel implementations don't call `cast_outputs()`, so when CPU temporaries were created to hold their outputs they weren't copied back to the out parameters correctly. Instead of fixing that issue, for simplicity this PR disables the behavior. The corresponding test in test_type_promotion.py is expanded with more operations to verify that unary ops can no longer have out arguments with different dtypes than their inputs (except in special cases like torch.abs which maps complex inputs to float outputs and torch.deg2rad which is secretly torch.mul).
Pull Request resolved: https://github.com/pytorch/pytorch/pull/41097
Differential Revision: D22422352
Pulled By: mruberry
fbshipit-source-id: 8e61d34ef1c9608790b35cf035302fd226fd9421
