Add test for glDrawPixels with depth-bound testing
Per mesa!7720 (comment 721754), add a test that tries to do glDrawPixels with depth-bounds testing enabled. Specifically, try a "simple" glDrawPixels that could be converted to a blit but that should be culled by the depth-bounds test. Based on looking at the code, I believe this will fail on Gallium drivers even before mesa!7720 (merged) lands.