[WebGPU] Implement direct copy for images. This CL implements CopyImage specifically in cases where the source is the same size and format as the destination. Bug: angleproject:438268609 Change-Id: Icf5f3685bb2f49874d996883c839515314f1c189 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/6842317 Commit-Queue: Liza Burakova <liza@chromium.org> Reviewed-by: Matthew Denton <mpdenton@chromium.org> Reviewed-by: Geoff Lang <geofflang@chromium.org>