Vulkan _SRGB formats have a suffix of _UNORM_SRGB in the corresponding
angle name.

Vulkan A2B10G10R10_*_PACK32 formats have angle names in the form
R10G10B10A2_*.

A16 and A32 formats are emulated similar to A8.

Some formats that are not in the front-end are removed.

Bug: angleproject:2364, angleproject:2405
Change-Id: I00718f450a374912d57d3c00ea167ce486e10aa0
Reviewed-on: https://chromium-review.googlesource.com/c/1468042Reviewed-by: Jamie Madill <jmadill@google.com>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Ian Elliott <ianelliott@google.com>
Commit-Queue: Ian Elliott <ianelliott@google.com>