playbin3: Propagate sink context
When the playsink's sink is activated its state is set to READY but it remains unlinked. So, in order for decodebin3 to potentially reuse the context later on, the whole playbin3 needs to have it internally stored.
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When the playsink's sink is activated its state is set to READY but it remains unlinked. So, in order for decodebin3 to potentially reuse the context later on, the whole playbin3 needs to have it internally stored.