deprecate closure-taking Props factories, see #3081

- base Props on Deploy, Class and Seq[Any] (i.e. constructor args)
- remove deprecated Props usage from akka-docs sample code
- rewrite UntypedActorDocTestBase
- rewrite Java/Scala doc section on actor creation
- add migration guide entry

akka-docs/rst/java/code/docs/camel/sample/route/CustomRouteSample.java

@@ -4,25 +4,16 @@ import akka.actor.*;
 import akka.camel.CamelExtension;
 
 public class CustomRouteSample {
+  @SuppressWarnings("unused")
   public static void main(String[] args) {
     try {
       //#CustomRouteExample
       // the below lines can be added to a Boot class, so that you can run the
       // example from a MicroKernel
       ActorSystem system = ActorSystem.create("some-system");
-      final ActorRef producer = system.actorOf(new Props(Producer1.class));
-      final ActorRef mediator = system.actorOf(new Props(new UntypedActorFactory() {
-        public Actor create() {
-          return new Transformer(producer);
-
-        }
-      }));
-      ActorRef consumer = system.actorOf(new Props(new UntypedActorFactory() {
-        public Actor create() {
-          return new Consumer3(mediator);
-
-        }
-      }));
+      final ActorRef producer = system.actorOf(Props.create(Producer1.class));
+      final ActorRef mediator = system.actorOf(Props.create(Transformer.class, producer));
+      final ActorRef consumer = system.actorOf(Props.create(Consumer3.class, mediator));
       CamelExtension.get(system).context().addRoutes(new CustomRouteBuilder());
       //#CustomRouteExample
     } catch (Exception e) {