xwayland: implement pixmap_from_buffers for the eglstream backend

Provides an implementation for the pixmap_from_buffers DRI3 function for
xwayland's eglstream backend. This will be used by the NVIDIA GLX driver
to pass buffers from client applications to the server. These can then
be presented using the PRESENT extension.

To hopefully make this less error-prone, we also introduce a "type"
field for this struct to distinguish between xwl_pixmaps for the new
DRI3-created pixmaps and those for the existing glamor-created pixmaps.

Additionally, the patch enables wnmd present mode with the eglstream backend.
This involves creating a wl_buffer for the provided dma-buf before importing it
into EGL and passing this to the compositor so it can be scanned out directly
if possible.

Since both backends now support this present mode, the HAS_PRESENT_FLIP flag is
no longer needed, so it can be removed.

Reviewed-by: Michel Dänzer <mdaenzer@redhat.com>
Acked-by: Olivier Fourdan <ofourdan@redhat.com>
Signed-off-by: Erik Kurzinger <ekurzinger@nvidia.com>
4 jobs for xwayland-eglstream-glx in 6 minutes and 18 seconds (queued for 2 seconds)
Status Name Job ID Coverage
  Docker Image
passed debian-buster #8707649

00:00:17

 
  Build And Test
passed autotools #8707650

00:06:00

passed meson #8707651

00:03:09

passed meson-noglamor #8707652

00:02:31