Make GstVaapiSurfaceProxy only a thin wrapper around a VA context and a
VA surface. i.e. drop any other attribute like timestamp, duration,
interlaced or top-field-first.
GstVaapiSurfaceProxy does not use any particular functionality from
GObject. Actually, it only needs a basic object type with reference
counting.
This is an API and ABI change.
Add new "interlaced" attribute to GstVaapiSurfaceProxy. Use this in
vaapipostproc so that to handles cases where bitstream is interlaced
but almost only frame pictures are generated. In this case, we should
not be alternating between top/bottom fields.