Merge pull request #17833 from akka/wip-deprecate-StepWise-∂π

move StepWise into tests and deprecate

akka-typed/src/main/scala/akka/typed/Behavior.scala

@@ -161,11 +161,6 @@ final case class Terminated(ref: ActorRef[Nothing]) extends Signal
  */
 object Failed {
 
-  /**
-   * Failure responses are in some cases communicated by using the companion
-   * objects of the wrapper behaviors, see the [[StepWise]] behavior for an
-   * example.
-   */
   sealed trait Decision
 
   @SerialVersionUID(1L)

akka-typed/src/test/scala/akka/typed/StepWise.scala

@@ -35,6 +35,7 @@ import scala.util.control.NonFatal
  * test procedures for actor systems, hence also the possibility to expect
  * failures (see [[StepWise.Steps#expectFailure]]).
  */
+@deprecated("to be replaced by process DSL", "2.4-M2")
 object StepWise {
   import Behavior._
   import ScalaDSL._