This CL also moves some comman code in d3d12::Adapter and
d3d11::Backend to d3d::Adapter and d3d::Backend, so it can be
shared with d3d11 backend.
Bug: dawn:1705
Change-Id: Ica3bf33232d3380b7d4799c77bf9b43a8374a66e
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/126220
Kokoro: Kokoro <noreply+kokoro@google.com>
Reviewed-by: Austin Eng <enga@chromium.org>
Commit-Queue: Peng Huang <penghuang@chromium.org>
Peng Huang