Add tests for RGB565, XRGB8888 and ARGB8888 pixel formats
This is to ensure that pixel formats RGB565, XRGB8888 and ARGB8888 are rendered correctly. Some tests already depend of XRGB and ARGB, but there are special cases to test for:
- RGB565 in general is not used yet
- with XRGB8888, ensure the X channel is really ignored, regardless of
- with ARGB8888, ensure the A channel is used outside of opaque region and ignored inside of opaque region
Ignoring A channel inside opaque region is not a protocol requirement but a workaround for Xwayland. Xwayland used to mess up in some cases by leaving garbage in the A channel.
This needs to run over both pixman and GL renderers. Hence this depends on #310 (closed) for infrastructure.