Polyfill this for the SPIR-V, HLSL and GLSL backends by replacing bgra8unorm with rgba8unorm, and swizzling.
Bug: tint:1804
Change-Id: I36638202840d7313001dff6c5b60dcb948988c34
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/117204
Commit-Queue: Ben Clayton <bclayton@google.com>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Kokoro: Kokoro <noreply+kokoro@google.com>