!per persistAsync

Breaks binary compatibility because adding new methods to Eventsourced
trait. Since akka-persistence is experimental this is ok, yet
source-level compatibility has been perserved thankfuly :-)

Deprecates:
* Rename of EventsourcedProcessor -> PersistentActor
* Processor -> suggest using PersistentActor
* Migration guide for akka-persistence is separate, as wel'll deprecate in minor versions (its experimental)
* Persistent as well as ConfirmablePersistent - since Processor, their
  main user will be removed soon.

Other changes:
* persistAsync works as expected when mixed with persist
* A counter must be kept for pending stashing invocations
* Uses only 1 shared list buffer for persit / persistAsync
* Includes small benchmark
* Docs also include info about not using Persistent() wrapper
* uses java LinkedList, for best performance of append / head on
  persistInvocations; the get(0) is safe, because these msgs only
  come in response to persistInvocations
* Renamed internal *MessagesSuccess/Failure messages because we kept
  small mistakes seeing the class "with s" and "without s" as the same
* Updated everything that refered to EventsourcedProcessor to
  PersistentActor, including samples

Refs #15227

Conflicts:
	akka-docs/rst/project/migration-guides.rst
	akka-persistence/src/main/scala/akka/persistence/JournalProtocol.scala
	akka-persistence/src/main/scala/akka/persistence/Persistent.scala
	akka-persistence/src/test/scala/akka/persistence/PersistentActorSpec.scala
	project/AkkaBuild.scala
+clu #15365 Make cluster.UniqueAddress public

(cherry picked from commit 2a2caeebd585d6dde53bbca0125e62626f7bae51)

Conflicts:
	akka-cluster/src/main/scala/akka/cluster/Member.scala
=con #15285 wrap message in RouterEnvelope before routing

PubSubMediator uses router which always unwraps RouterEnvelope messages.
However unwrapping is undesirable if user sends message in
ConsistentHashableEnvelope. Thus PubSubMediator should always wrap user
messages in RouterEnvelope which will be unwrapped by the router, leaving
user message unchanged.

Also disallow consistent hashing routing logic in pub-sub mediator.
Merge pull request #15380 from ktoso/port-persistAsync

!per PersistentActor#persistAsync (forward port)
Merge pull request #15382 from akka/wip-15365-UniqueAddress-master-patriknw

+clu #15365 Make cluster.UniqueAddress public (for validation)
+per #13944 Send RecoveryComplete message at end of recovery

Fixes #13944

Conflicts:
	akka-docs/rst/scala/code/docs/persistence/PersistenceDocSpec.scala
	akka-persistence/src/main/scala/akka/persistence/Processor.scala
	project/AkkaBuild.scala
Merge pull request #15362 from 2m/pubsub-wrap-before-routing

=con #15285 wrap message in RouterEnvelope before routing (for validation)
Merge pull request #15385 from akka/wip-13944-send-marker-message-after-recovery-finished-master-ban

+per #13944 Send RecoveryComplete message at end of recovery (Validation)
Merge remote-tracking branch: upstream/master