Backport of "playbin3: various fixes" into 1.20
Partial backport of !1900 (merged) "playbin3 : Improve selection and reusability".
Commits:
- 67dbe757 playsink: Fix reconfiguration after removing text_sink
- 9ebb4505 playbin3: Reconfigure on streams-selected message.
- 52d9614d playbin3: Hold playbin lock on pad-added
-
9b94798d parsebin: Implement ACCEPT_CAPS handling(dropped, not backported) -
c658e29d decodebin3: Convert checks to assertions(dropped, not backported) -
4a436b5c decodebin3: Reset parsebin when new caps arrive(dropped, not backported) - 90426f57 playbin3: Remove stale code