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.
If the runners require multiple calls to run_shader_tests() for
different shader model ranges, these are moved inside the sole runner
call.
For the same reason, the trace() messages are also moved inside the
runner calls.
