xrt: Introduce xrt_system_compositor
This change introduces a xrt_system_compositor, it is basically a analogous to XrSystemID but instead of being a fully fledged xrt_system this is only the compositor part of it.
This change introduces a xrt_system_compositor, it is basically a analogous to XrSystemID but instead of being a fully fledged xrt_system this is only the compositor part of it.