Vulkan: Add GetColorComponentFlags. This small helper routine will be used when doing masked clears. Bug: angleproject:2455 Change-Id: Id309b48f2bc5958abb1276d140c9a3599fb7d2b9 Reviewed-on: https://chromium-review.googlesource.com/1024825 Reviewed-by: Luc Ferron <lucferron@chromium.org> Reviewed-by: Geoff Lang <geofflang@chromium.org> Commit-Queue: Jamie Madill <jmadill@chromium.org>