=str #16095 make Actor{Publisher,Subscriber} as {Source,Sink}

* Props{Source,Sink} creates an actor from props as a child
of StreamSupervisor actor and wraps it into {Publisher,Subscriber}
* ActorRef{Source,Sink} wraps a given ActorRef into {Publisher,Subscriber}
* In both cases user actor should one of akka.stream.actor.Actor{Publisher,Subscriber}

Fixes #16095
I think that you are right that we should only provide the one that takes the props. That would make things more explicit and less surprising if the flow gets reused.