[iOS GPU] Use setTexture() rather than copyTexture() (#56069)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/56069
It's more efficient to capture a MPSImage object than copying a one from outside.
ghstack-source-id: 126552396
Test Plan:
- All operator tests pass
- Sandcastle
- CircleCI
Reviewed By: SS-JIA
Differential Revision: D27694542
fbshipit-source-id: e1bbbffc3f8c109816cb117aebd0aae8576c6c5c
