anv/wsi/x11: abstract WSI interface from internals.
anv/wsi/x11: abstract WSI interface from internals.

This allows the API and the internals to be split, and the
internals shared.

Reviewed-by: Jason Ekstrand <68c46a606457643eab92053c1c05574abb26f861@jlekstrand.net>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler