Metal: Implement CHROMIUM_copy_texture Bug: angleproject:4930 Bug: angleproject:2634 Change-Id: I9fd958aa1dd872855be06a14bdbba4c6624dc934 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2340396 Commit-Queue: Jonah Ryan-Davis <jonahr@google.com> Reviewed-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Jonah Ryan-Davis <jonahr@google.com>