xwayland: Fall back to GLES2 if we don't get at least GL 2.1 in glamor

Some particularly unfortunate hardware (Intel gen3, mostly) will give
you GLES2 but not GL 2.1. Fall back to GLES2 for such cases so you still
get accelerated GLX.
3 jobs for xwayland-glamor-gles2-fallback in 5 minutes and 58 seconds (queued for 36 seconds)
Status Job ID Name Coverage
  Docker Image
passed #887463
debian-testing

00:00:36

 
  Build And Test
passed #887464
autotools-build-and-test

00:05:22

passed #887465
meson-build-and-test

00:01:47