Migrate D3D ClearParameters struct to the new color mask storage

Bug: angleproject:4394
Change-Id: Ibeb64e4bbb2758b9c8271fc3c59d2d675850b0a8
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2165886
Commit-Queue: Kenneth Russell <kbr@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>