This call cannot fail, but needs cleanup if others fail.  By moving it
to the end, we eliminate some cleanup.

Moved code from AudioOutputControl::InternalOpen2().

struct AudioOutput should not know or care about multi-threading.

Prepare for moving the AudioOutputSource to class AudioOutputControl.

That function is "noexcept".

This allows removing the "base.pause" check from the JACK output
plugin, and will allow removing similar accesses from other plugins.

The AudioOutput struct (which is exposed to all plugins) should not be
aware that it's being controlled by another thread.

Will move attributes from struct AudioOutput that are specific to the
OutputThread.  The new struct AudioOutputControl is a holder for the
AudioOutput pointer.

This prepares for making the output list more dynamic, to allow moving
outputs to between partitions.