tests: Add UAV format-specific require directives and cap checks.
Supersedes !966 (closed), now requiring and checking support for individual UAV formats as suggested.
Marked as a Draft because I am not totally sure that I am checking for the support correctly on 5/6 for all of the pertinent backends, but it works on my machine:tm: (Intel UHD Graphics 770) as expected, the supported/unsupported UAV formats are consistent across them.