playbin: Propagate sink context

Any contexts created by sink during activation need to be propagated to whole elements of playbin.

Similar to !384 (merged)

When application passed d3d11videosink to playbin, the d3d11context created by d3d11videosink does not propagated to decodebin. The context is required for a d3d11*dec element to share resources among decoder and sink.

Looks good to me but the same should probably be done also for playbin3?

resolved all threads

assigned to @gstreamer-merge-bot

assigned to @seungha.yang and unassigned @gstreamer-merge-bot

I couldn't merge this branch: It is taking too long to see the request marked as merged!

merged

changed milestone to %1.17.1

mentioned in issue gst-editing-services#131 (moved)

mentioned in issue gstreamer#4005 (closed)