screen-cast/stream: Add DMABUF-only record flag

Next commits will reintroduce a certain behavior of stage
capturing that can only happen with DMA-BUF buffers. To
control this, add a new flag tp MetaScreenCastRecordFlags
for this behavior.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2186>

(cherry picked from commit 8fe45d77)