[Backport to xwayland-21-1] xwayland/eglstream: Prefer EGLstream if available
This is to backport a few commits from master for Xwayland and glamor/eglstream, namely:
6dd9709b xwayland/eglstream: Prefer EGLstream if available
c5d1fed9 xwayland/glamor: Log backend selected for debug
30d0d4a1 xwayland/glamor: Change errors to verbose messages
96c82bef xwayland/eglstream: Demote EGLstream device warning