xwayland: Add EGL-backed GLX provider

Without this we're using driswrast to set up GLX visuals. This is
unfortunate because llvmpipe does not expose multisample configs, so
various apps that expect them will fail. With this we just query the
capabilities of the EGL that's backing glamor, and reflect that to the
GLX clients. This also paves the way for xserver to stop being a DRI
driver loader, which is nice.

Fixes: xorg/xserver#640
Fixes: xorg/xserver#643
Fixes: https://bugs.freedesktop.org/show_bug.cgi?id=98272
Reviewed-by: Olivier Fourdan <ofourdan@redhat.com>
Signed-off-by: Adam Jackson <ajax@redhat.com>
3 jobs for glxegl in 6 minutes and 24 seconds (queued for 1 second)
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passed meson-build-and-test #314463