Add first-field (FF) flag to GstVaapiPicture, thus not requiring is_first_field
member in each decoder. Rather, when a GstVaapiPicture is created, it is considered
as the first field. Any subsequent allocated field will become the second field.
Add gst_vaapi_picture_new_field() function that clones a picture, while
preserving the parent picture surface. i.e. the surface proxy reference
count is increased and other fields copied as is. Besides, the picture
is reset into a "non-output" mode.
Add top-field-first (TFF) and interlaced flags to GstVaapiPicture so they
could be propagated to the surface proxy when it is pushed for rendering.
Besides, top and bottom fields are now expressed with picture structure flags
from GstVaapiSurfaceRenderFlags.
If GstVaapiPicture has flag SKIPPED set, this means gst_vaapi_picture_output()
will not push the underlying surface for rendering. Besides, VC-1 skipped P-frame
has nothing to do with rendering. This only means that the currently decoded
picture is just a copy of its reference picture.
Keep a valid reference to the proxy in GstVaapiPicture so that frames
marked as "used for reference" could be kept during the lifetime of the
picture. i.e. don't release them too soon as they could be re-used right
away.
The new API simplifies a lot reference counting and makes it more
flexible for future additions/changes. The GstVaapiCodecInfo is
also gone. Rather, new helper macros are provided to allocate
picture, slice and quantization matrix parameter buffers.
