[PyTorch] Allow copy operations on MaybeOwned (#55419)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/55419
Turns out it's useful to have these. I chose to implement them in the straightforward safe way, rather than always borrowing.
ghstack-source-id: 126369328
Test Plan: Added more automated tests.
Reviewed By: hlu1
Differential Revision: D27545805
fbshipit-source-id: 84bb4458b86672ad340cc1f0aa18b80ca7ee13f1
