Adds the CopySrc and CopyDst usages to swapchain textures when
available in backends so that the wgpu::Texture returned from
GetCurrentTexture can be used in copies.
Also adds a swapchain tests to check that these usages indeed
work.
Bug: dawn:1551
Change-Id: I8495075b0bfb5b8dd953a7811a9d75a76096b143
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/133464
Reviewed-by: Austin Eng <enga@chromium.org>
Commit-Queue: Corentin Wallez <cwallez@chromium.org>
Kokoro: Kokoro <noreply+kokoro@google.com>