=str #22584 make subfusing work if diff materialize() is called

Also: removed unecessary method with wrong name, #22350

akka-distributed-data/src/main/scala/akka/cluster/ddata/ORMultiMap.scala

@@ -22,7 +22,6 @@ object ORMultiMap {
    * Java API
    */
   def create[A, B](): ORMultiMap[A, B] = empty[A, B]
-  def createWithDeltaDelta[A, B](): ORMultiMap[A, B] = emptyWithValueDeltas[A, B]
 
   /**
    * Extract the [[ORMultiMap#entries]].

akka-stream/src/main/scala/akka/stream/impl/ActorMaterializerImpl.scala

@@ -96,7 +96,14 @@ private[akka] class SubFusingActorMaterializerImpl(val delegate: ExtendedActorMa
   override def executionContext: ExecutionContextExecutor = delegate.executionContext
 
   override def materialize[Mat](runnable: Graph[ClosedShape, Mat]): Mat =
-    delegate.materialize(runnable)
+    delegate match {
+      case am: PhasedFusingActorMaterializer ⇒
+        materialize(runnable, am.defaultInitialAttributes)
+
+      case other ⇒
+        throw new IllegalStateException(s"SubFusing only supported by [PhasedFusingActorMaterializer], " +
+          s"yet was used with [${other.getClass.getName}]!")
+    }
 
   override def materialize[Mat](runnable: Graph[ClosedShape, Mat], initialAttributes: Attributes): Mat = {
     if (PhasedFusingActorMaterializer.Debug) println(s"Using [${getClass.getSimpleName}] to materialize [${runnable}]")

akka-stream/src/main/scala/akka/stream/impl/PhasedFusingActorMaterializer.scala

@@ -365,7 +365,8 @@ private final case class SavedIslandData(islandGlobalOffset: Int, lastVisitedOff
 
   private[this] def createFlowName(): String = flowNames.next()
 
-  private val defaultInitialAttributes = {
+  /** INTERNAL API */
+  private[akka] val defaultInitialAttributes = {
     val a = Attributes(
       Attributes.InputBuffer(settings.initialInputBufferSize, settings.maxInputBufferSize) ::
         ActorAttributes.SupervisionStrategy(settings.supervisionDecider) ::