Add missing files to Dawn build

This adds the RenderPassBuilderD3D12 files and ignores a narrowing error in them.

Change-Id: Ie9ebc1608ad6bbbc48e0f1cd8d54a9213d9836a4
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/278777
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
1 file changed