The used UAV formats are explicitly added in the [require] section of
every test that uses them.
Some of these tests were failing on Intel UHD graphics 770 because of
missing support for additional UAV load types, explicitly requiring
these formats allows these tests to be skipped.
The current default is r32g32b32a32 but it requires special support
which is not available on all GPUs, so it is not a very convenient
default.
Instead of changing the default making it different from RTV resoures,
the format is required to always be explicit for UAVs.
The exceptions are counter_buffer and buffers with "stride", which don't
require a format because it is already implied.
If in the same shader_test file we have both a [buffer uav n] and a
[uav n] with the same slot "n", we want the last one to override the
first one instead of passing both resources to the backends.
Same for [buffer srv n] and [texture n] after we introduce SRV buffers.
