Record the underlying native display instance into the toplevel
GstVaapiDisplay object. This is useful for fast lookups to the
underlying native display, e.g. for creating an EGL display.
Fix formts for various GST_DEBUG et al. invocations. More precisely,
make size_t arguments use the %zu format specifier accordingly; force
XID formats to be a 32-bit unsigned integer; and fix the format used
for gst_vaapi_create_surface_with_format() error cases since we have
been using strings nowadays.
Implement the new render-to-pixmap API. The only supported pixmap format
that will work is xRGB, with native byte ordering. Others might work but
they were not tested.
