+per #13944 Send RecoveryComplete message at end of recovery

Fixes #13944
Merge pull request #15350 from akka/wip-13944-send-marker-message-after-recovery-finished-ban

+per #13944 Send RecoveryComplete message at end of recovery
=per #13962 Close LevelDB snapshots to avoid resource leakage
=per #13898 Make LocalSnapshotStore directory creation more robust
Merge pull request #15329 from akka/wip-13962-investigate-leveldb-compaction-issue-ban

=per #13962 Close LevelDB snapshots to avoid resource leakage
Merge pull request #15374 from akka/wip-13898-failed-SharedLeveldbJournalSpec-ban

=per #13898 Make LocalSnapshotStore directory creation more robust
+per #15229 defer for PersistentActor

* Deferred events are not persisted, thus will not participate in replays
  etc. If users want events to be persisted, they can simply use
  `persistAsync` instead.
* This, 3rd, rewrite extends the Persistent hierarchy by a top level
  trait "Resequenceable", which is used to mark every event to be sent
  in sequence back to the PersistentActor. These are split into
  NonPersistentRepr or PersistentRepr, and acted upon accordingly.
* defer is guaranteed to be called, even after persistence failures
* Includes docs updates for java/scala/java8

Resolves #15229
Depends on #15227
Merge pull request #15339 from ktoso/per-defer-persistentactor-ktoso

+per defer for PersistentActor
+clu #15365 Make cluster.UniqueAddress public