Add GstVideoMultiviewFramePacking enum, and the
video-multiview-mode and video-multiview-flags
properties on playbin.
Use a pad probe to replace the multiview information in
video caps sent out from uridecodebin.
This is a part implementation only - for full
correctness, it should also modify caps in caps events,
accept-caps and allocation queries.
https://bugzilla.gnome.org/show_bug.cgi?id=611157
383d8f02be