This class provides a set of compute-based internal utilities.
Currently, buffer clear and copy are implemented.  Other possibilities
include more efficient mip map generation, or specialized texture
operations.

VertexArrayVk::updateIndexTranslation() is updated to convert the
GL_UNSIGNED_BYTE index buffer to a GL_UNSIGNED_SHORT one using this
class to avoid a CPU readback.

The vk::Format class is augmented with a few flags (IsInt, IsUnsigned)
to be able to select the appropriate shader based on the format (float,
int or uint).

Bug: angleproject:2958,angleproject:3003
Change-Id: Ie35519deb3c32a3da5ccf74080c70092c9287f0a
Reviewed-on: https://chromium-review.googlesource.com/c/1336307
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>