DispatchUtilsVk is renamed to UtilsVk and the functionality in
framebuffer's clearWithDraw() is moved to that class.  Eventually, more
fragment-shader-based internal algorithms will be added to this class as
well.

Bug: angleproject:2958
Change-Id: I4753c9cb3288b59cd1ed60fe7a57b9f189704322
Reviewed-on: https://chromium-review.googlesource.com/c/1369284
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>