[GPU] Add metal to DispatchKeySet (#46455)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/46455
After this PR(https://github.com/pytorch/pytorch/pull/46236 ) landed, the `aten::copy_` can no longer be dispatched to Metal kernels.
ghstack-source-id: 114499399
Test Plan:
- Sandcastle CI
- Circle CI
Reviewed By: IvanKobzarev, ailzhang
Differential Revision: D24356769
fbshipit-source-id: 8660ca5be663fdc8985d9eb710ddaadbb43b0ddd
