replace unicode arrows

* ⇒, →, ←
* because we don't want to show them in documentation snippets and
  then it's complicated to avoid that when snippets are
  located in src/test/scala in individual modules
* dont replace object `→` in FSM.scala and PersistentFSM.scala

akka-stream/src/main/scala/akka/stream/impl/streamref/SourceRefImpl.scala

@@ -21,7 +21,7 @@ import scala.concurrent.{ Future, Promise }
 @InternalApi
 private[stream] final case class SourceRefImpl[T](initialPartnerRef: ActorRef) extends SourceRef[T] {
   def source: Source[T, NotUsed] =
-    Source.fromGraph(new SourceRefStageImpl(OptionVal.Some(initialPartnerRef))).mapMaterializedValue(_ ⇒ NotUsed)
+    Source.fromGraph(new SourceRefStageImpl(OptionVal.Some(initialPartnerRef))).mapMaterializedValue(_ => NotUsed)
 }
 
 /**
@@ -33,15 +33,15 @@ private[stream] final case class SourceRefImpl[T](initialPartnerRef: ActorRef) e
 @InternalApi
 private[stream] final class SourceRefStageImpl[Out](
   val initialPartnerRef: OptionVal[ActorRef]
-) extends GraphStageWithMaterializedValue[SourceShape[Out], Future[SinkRef[Out]]] { stage ⇒
+) extends GraphStageWithMaterializedValue[SourceShape[Out], Future[SinkRef[Out]]] { stage =>
 
   val out: Outlet[Out] = Outlet[Out](s"${Logging.simpleName(getClass)}.out")
   override def shape = SourceShape.of(out)
 
   private def initialRefName =
     initialPartnerRef match {
-      case OptionVal.Some(ref) ⇒ ref.toString
-      case _                   ⇒ "<no-initial-ref>"
+      case OptionVal.Some(ref) => ref.toString
+      case _                   => "<no-initial-ref>"
     }
 
   override def createLogicAndMaterializedValue(inheritedAttributes: Attributes): (GraphStageLogic, Future[SinkRef[Out]]) = {
@@ -127,7 +127,7 @@ private[stream] final class SourceRefStageImpl[Out](
         scheduleOnce(DemandRedeliveryTimerKey, settings.demandRedeliveryInterval)
 
       override protected def onTimer(timerKey: Any): Unit = timerKey match {
-        case SubscriptionTimeoutTimerKey ⇒
+        case SubscriptionTimeoutTimerKey =>
           val ex = StreamRefSubscriptionTimeoutException(
             // we know the future has been competed by now, since it is in preStart
             s"[$stageActorName] Remote side did not subscribe (materialize) handed out Sink reference [${promise.future.value}]," +
@@ -135,25 +135,25 @@ private[stream] final class SourceRefStageImpl[Out](
 
           throw ex // this will also log the exception, unlike failStage; this should fail rarely, but would be good to have it "loud"
 
-        case DemandRedeliveryTimerKey ⇒
+        case DemandRedeliveryTimerKey =>
           log.debug("[{}] Scheduled re-delivery of demand until [{}]", stageActorName, localCumulativeDemand)
           getPartnerRef ! StreamRefsProtocol.CumulativeDemand(localCumulativeDemand)
           scheduleDemandRedelivery()
 
-        case TerminationDeadlineTimerKey ⇒
+        case TerminationDeadlineTimerKey =>
           failStage(RemoteStreamRefActorTerminatedException(s"Remote partner [$partnerRef] has terminated unexpectedly and no clean completion/failure message was received " +
             "(possible reasons: network partition or subscription timeout triggered termination of partner). Tearing down."))
       }
 
-      lazy val initialReceive: ((ActorRef, Any)) ⇒ Unit = {
-        case (sender, msg @ StreamRefsProtocol.OnSubscribeHandshake(remoteRef)) ⇒
+      lazy val initialReceive: ((ActorRef, Any)) => Unit = {
+        case (sender, msg @ StreamRefsProtocol.OnSubscribeHandshake(remoteRef)) =>
           cancelTimer(SubscriptionTimeoutTimerKey)
           observeAndValidateSender(remoteRef, "Illegal sender in SequencedOnNext")
           log.debug("[{}] Received handshake {} from {}", stageActorName, msg, sender)
 
           triggerCumulativeDemand()
 
-        case (sender, msg @ StreamRefsProtocol.SequencedOnNext(seqNr, payload: Out @unchecked)) ⇒
+        case (sender, msg @ StreamRefsProtocol.SequencedOnNext(seqNr, payload: Out @unchecked)) =>
           observeAndValidateSender(sender, "Illegal sender in SequencedOnNext")
           observeAndValidateSequenceNr(seqNr, "Illegal sequence nr in SequencedOnNext")
           log.debug("[{}] Received seq {} from {}", stageActorName, msg, sender)
@@ -161,7 +161,7 @@ private[stream] final class SourceRefStageImpl[Out](
           onReceiveElement(payload)
           triggerCumulativeDemand()
 
-        case (sender, StreamRefsProtocol.RemoteStreamCompleted(seqNr)) ⇒
+        case (sender, StreamRefsProtocol.RemoteStreamCompleted(seqNr)) =>
           observeAndValidateSender(sender, "Illegal sender in RemoteSinkCompleted")
           observeAndValidateSequenceNr(seqNr, "Illegal sequence nr in RemoteSinkCompleted")
           log.debug("[{}] The remote stream has completed, completing as well...", stageActorName)
@@ -170,22 +170,22 @@ private[stream] final class SourceRefStageImpl[Out](
           completed = true
           tryPush()
 
-        case (sender, StreamRefsProtocol.RemoteStreamFailure(reason)) ⇒
+        case (sender, StreamRefsProtocol.RemoteStreamFailure(reason)) =>
           observeAndValidateSender(sender, "Illegal sender in RemoteSinkFailure")
           log.warning("[{}] The remote stream has failed, failing (reason: {})", stageActorName, reason)
 
           self.unwatch(sender)
           failStage(RemoteStreamRefActorTerminatedException(s"Remote stream (${sender.path}) failed, reason: $reason"))
 
-        case (_, Terminated(ref)) ⇒
+        case (_, Terminated(ref)) =>
           partnerRef match {
-            case OptionVal.Some(`ref`) ⇒
+            case OptionVal.Some(`ref`) =>
               // we need to start a delayed shutdown in case we were network partitioned and the final signal complete/fail
               // will never reach us; so after the given timeout we need to forcefully terminate this side of the stream ref
               // the other (sending) side terminates by default once it gets a Terminated signal so no special handling is needed there.
               scheduleOnce(TerminationDeadlineTimerKey, settings.finalTerminationSignalDeadline)
 
-            case _ ⇒
+            case _ =>
               // this should not have happened! It should be impossible that we watched some other actor
               failStage(RemoteStreamRefActorTerminatedException(s"Received UNEXPECTED Terminated($ref) message! " +
                 s"This actor was NOT our trusted remote partner, which was: $getPartnerRef. Tearing down."))
@@ -214,12 +214,12 @@ private[stream] final class SourceRefStageImpl[Out](
       /** @throws InvalidPartnerActorException when partner ref is invalid */
       def observeAndValidateSender(partner: ActorRef, msg: String): Unit =
         partnerRef match {
-          case OptionVal.None ⇒
+          case OptionVal.None =>
             log.debug("Received first message from {}, assuming it to be the remote partner for this stage", partner)
             partnerRef = OptionVal(partner)
             self.watch(partner)
 
-          case OptionVal.Some(ref) ⇒
+          case OptionVal.Some(ref) =>
             if (partner != ref) {
               val ex = InvalidPartnerActorException(partner, getPartnerRef, msg)
               partner ! StreamRefsProtocol.RemoteStreamFailure(ex.getMessage)