* Change priority of DNS resolved addresses based on java.net.preferIPv6Addresses property. #22330
* Include test specs for IPv6 resolver selection. #22330
* Use Java system properties to retrieve the IPv6 preference. #22330
(cherry picked from commit 6406c0ed95bf295b27bbb0e7e8e228f5979a1336)
* because with Scala 2.12 it can't infer the right overload
* prefer the `() =>`, but here it's clear that it's a callback
* similar in ActorSystem.registerOnTermination
* e.g. the jvm shutdown hook should be installed immediately
* noticed that it was initialized from artery shutdown
* run-by-jvm-shutdown-hook=off in multi-jvm tests
* Receive class that wraps PartialFunction, to avoid
scary scala types
* move AbstractActorContext to AbstractActor.ActorContext
* converting docs, many, many UntypedActor
* removing UntypedActor docs
* add unit test for ReceiveBuilder
* MiMa filters
* consistent use of getContext(), self(), sender()
* rename cross references
* migration guide
* skip samples for now
* improve match type safetyi, add matchUnchecked
* the `? extends P` caused code like this to compile:
`match(String.class, (Integer i) -> {})`
* added matchUnchecked, since it can still be useful (um, convenient)
to be able to do:
`matchUnchecked(List.class, (List<String> list) -> {})`
* eleminate some scala.Option
* preRestart
* findChild
* ActorIdentity.getActorRef
* CoordinatedShutdown that can run tasks for configured phases in order (DAG)
* coordinate handover/shutdown of singleton with cluster exiting/shutdown
* phase config obj with depends-on list
* integrate graceful leaving of sharding in coordinated shutdown
* add timeout and recover
* add some missing artery ports to tests
* leave via CoordinatedShutdown.run
* optionally exit-jvm in last phase
* run via jvm shutdown hook
* send ExitingConfirmed to leader before shutdown of Exiting
to not have to wait for failure detector to mark it as
unreachable before removing
* the unreachable signal is still kept as a safe guard if
message is lost or leader dies
* PhaseClusterExiting vs MemberExited in ClusterSingletonManager
* terminate ActorSystem when cluster shutdown (via Down)
* add more predefined and custom phases
* reference documentation
* migration guide
* problem when the leader order was sys2, sys1, sys3,
then sys3 could not perform it's duties and move Leving sys1 to
Exiting because it was observing sys1 as unreachable
* exclude Leaving with exitingConfirmed from convergence condidtion
* to be able to introduce new messages and still support rolling upgrades,
i.e. a cluster of mixed versions
* note that it's only catching NotSerializableException, which we already
use for unknown serializer ids and class manifests
* note that it is not catching for system messages, since that could result
in infinite resending
