This is useful after a freewheel export, where a realtime-stop
is called, but the actual Locate/MustStop event is only processed
later. Once the session switches back to normal processing after
export the transport is still rolling, TSFM schedules a de-click
locate. This may play some remaining audio.
This new API allows to hard stop the transport, without going
via any session-events and process_with_events. It is intended to
be called from the freewheel process-callback in the last export
cycle.
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