+str #15205 Java API for FlexiRoute

Conflicts:
	akka-stream/src/main/scala/akka/stream/impl/ActorBasedFlowMaterializer.scala
+str #16105 Java API for FlexiMerge

Conflicts:
	akka-stream/src/main/scala/akka/stream/impl/ActorBasedFlowMaterializer.scala
added Java DSL