GstVaapiPixmap is an abstract base class which only implementation
were GstVaapiPixmapX11. This class were used for a special type of
rendering in the tests apps, utterly unrelated in GStreamer.
Since gstreamer-vaapi is no longer a general-user wrapper for VA-API
we should remove this unused API.
This removal drops libxrender dependency.
This is another step in the gobjectification of the internal library
of gstreamer-vaapi. Now it is the turn of GstVaapiWindow and its
derivates.
The idea is to minimize the changeset keeping the same design as
much as possible.
GstVaapiWindow is defined as an abstract class with two properties:
the GstVaapiDisplay and the native ID. Thus, many of the
GstVaapiObject macros were copied as GstVaapiWindow macros.
The function gst_vaapi_window_new_internal() is kept as a decorator
of for calling gst_vaapi_window_create() and the possibility of
failure.
The descendant classes, such as glx, still use the private
structures, but through the gobject mechanism.
When creating a GstVaapiWindowEGL, it also creates native window by its own
native display. It should pass the native display, either X11 or Wayland.
https://bugzilla.gnome.org/show_bug.cgi?id=768266
