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.
