Vulkan: Implement transfer path for texture copy This is primarily in preparation for compressed texture copy, but has the following side effect: - When transfer is possible, it's faster than draw - When texture format does not support draw (but transfer is possible), it will avoid copying through CPU. Bug: angleproject:2670 Change-Id: I49e1b51e6ccec875db3f971106687c7d48c4916f Reviewed-on: https://chromium-review.googlesource.com/c/1470595 Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org> Reviewed-by: Yuly Novikov <ynovikov@chromium.org>