Get the clock pointer using the io_changed stream event.
and update the clock before triggering the process
The clock needs to be updated in the data loop thread
and before triggering the process so move the calls to
`pw_stream_trigger_process` from gstreamer thread context
into the data loop thread context by invoking a callback
and update the clock inside the data loop callback
before the trigger
Construct this new class from both the src and sink to be able to share code
Consolidate the previous mess of open/close/start/stop into a single pair
of open/close functions in the new stream class
