Introduce warning silencer plugin (#26588)

So now we can compile akka-distributed-data with
-Xfatal-warnings - though I'm not yet sure about
enabling the (other) undisciplineScalacOptions

* Fix multi-node silencing
* Fix scaladoc warnings
* Introduce annotation to declare ccompat use
* Add explicit toString
* Fix deprecation on 2.13
* Move 'immutable' ccompat helpers to shared ccompat package
* Add MiMa for internal scala 2.13 compatibility class
* Internal API markers
* Fix scaladoc generation
Got bitten by https://github.com/scala/bug/issues/11021

akka-distributed-data/src/multi-jvm/scala/akka/cluster/ddata/DurablePruningSpec.scala

@@ -16,8 +16,9 @@ import akka.actor.ActorSystem
 import akka.actor.ActorRef
 import scala.concurrent.Await
 import akka.cluster.MemberStatus
-import akka.util.ccompat.imm._
+import akka.util.ccompat._
 
+@ccompatUsedUntil213
 object DurablePruningSpec extends MultiNodeConfig {
   val first = role("first")
   val second = role("second")
@@ -75,6 +76,7 @@ class DurablePruningSpec extends MultiNodeSpec(DurablePruningSpec) with STMultiN
 
       val sys2 = ActorSystem(system.name, system.settings.config)
       val cluster2 = Cluster(sys2)
+      val distributedData2 = DistributedData(sys2)
       val replicator2 = startReplicator(sys2)
       val probe2 = TestProbe()(sys2)
       Cluster(sys2).join(node(first).address)
@@ -98,7 +100,9 @@ class DurablePruningSpec extends MultiNodeSpec(DurablePruningSpec) with STMultiN
       replicator ! Update(KeyA, GCounter(), WriteLocal)(_ :+ 3)
       expectMsg(UpdateSuccess(KeyA, None))
 
-      replicator2.tell(Update(KeyA, GCounter(), WriteLocal)(_.increment(cluster2, 2)), probe2.ref)
+      replicator2.tell(
+        Update(KeyA, GCounter(), WriteLocal)(_.increment(distributedData2.selfUniqueAddress, 2)),
+        probe2.ref)
       probe2.expectMsg(UpdateSuccess(KeyA, None))
 
       enterBarrier("updates-done")

akka-distributed-data/src/multi-jvm/scala/akka/cluster/ddata/ReplicatorMapDeltaSpec.scala

@@ -331,7 +331,7 @@ class ReplicatorMapDeltaSpec extends MultiNodeSpec(ReplicatorMapDeltaSpec) with
 
       enterBarrier("replicated-2")
       // no OversizedPayloadException logging
-      errorLogProbe.expectNoMsg(100.millis)
+      errorLogProbe.expectNoMessage(100.millis)
 
       enterBarrierAfterTestStep()
     }

akka-distributed-data/src/multi-jvm/scala/akka/cluster/ddata/ReplicatorPruningSpec.scala

@@ -239,7 +239,7 @@ class ReplicatorPruningSpec extends MultiNodeSpec(ReplicatorPruningSpec) with ST
 
       // after full replication should still not be able to update with data from removed node
       // but it would not work after removal of the PruningPerformed markers
-      expectNoMsg(maxPruningDissemination + 3.seconds)
+      expectNoMessage(maxPruningDissemination + 3.seconds)
 
       runOn(first) {
         updateAfterPruning(expectedValue = 12)