=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 was referring to the wrapping done here:

    (akka.stream.actor.ActorSubscriber[In](subscriberRef), subscriberRef).

Although it is possible to have a Sink that would be materialized to ActorPublisher, I think ActorSubscriber is more idiomatic.