Issue: SPR-12730

Issue: SPR-12724

Issue: SPR-12724

Issue: SPR-12655

Add support for annotation-based event listeners. Enabled automatically
when using Java configuration or can be enabled explicitly via the
regular <context:annotation-driven/> XML element. Detect methods of
managed beans annotated with @EventListener, either directly or through
a meta-annotation.

Annotated methods must define the event type they listen to as a single
parameter argument. Events are automatically filtered out according to
the method signature. When additional runtime filtering is required, one
can specify the `condition` attribute of the annotation that defines a
SpEL expression that should match to actually invoke the method for a
particular event. The root context exposes the actual `event`
(`#root.event`) and method arguments (`#root.args`). Individual method
arguments are also exposed via either the `a` or `p` alias (`#a0` refers
to the first method argument). Finally, methods arguments are exposed via
their names if that information can be discovered.

Events can be either an ApplicationEvent or any arbitrary payload. Such
payload is wrapped automatically in a PayloadApplicationEvent and managed
explicitly internally. As a result, users can now publish and listen
for arbitrary objects.

If an annotated method has a return value, an non null result is actually
published as a new event, something like:

@EventListener
public FooEvent handle(BarEvent event) { ... }

Events can be handled in an aynchronous manner by adding `@Async` to the
event method declaration and enabling such infrastructure. Events can
also be ordered by adding an `@order` annotation to the event method.

Issue: SPR-11622

Prior to this change when adding subscriptions
DefaultSubscriptionRegistry (incorrectly) made a copy of the given map
for its "access" cache rather than for its "update" cache.

Issue: SPR-12665

Issue: SPR-12615

This change removes the need for the isStreaming field from the base
class AbstractHttpSockJsSession. This field was used to account for
differences between polling vs streaming SockJS sessions without having
to expose to sub-classes private fields that are otherwise protected
from concurrent access by the base class. The change manages to delegate
to sub-classes without providing direct access to protected fields.

Issue: SPR-12427

The test was verifying that when a DISCONNECT frame is sent to the
broker, there will be no further messages on the clientOutboundChannel.

This is generally true, however in some cases when the broker receives
a DISCONNECT it may close its connection fast enough (before we do) in
which case we send an ERROR message downstream to ensure the WebSocket
side is cleaned up. Either way the downstream should be idempotent
with regards to cleaning up sessions.

Issue: SPR-12567

With this commit, Jackson builder is now used in spring-websocket
to create the ObjectMapper instance.

It is not possible to use the builder for spring-messaging
and spring-jms since these modules don't have a dependency on
spring-web, thus they now just customize the same features:
 - MapperFeature#DEFAULT_VIEW_INCLUSION is disabled
 - DeserializationFeature#FAIL_ON_UNKNOWN_PROPERTIES is disabled

Issue: SPR-12293

Issue: SPR-12479

Issue: SPR-12484

Issue: SPR-12431

Issue: SPR-12406

This commit fixes the parsing of message destinations such as
"/user/anna/queue/foo", reverting a regression introduced by SPR-11506,
which worked well with @SendToUser use cases but caused issues for
messages sent to other users.

Issue: SPR-12444

Issue: SPR-12418

Before this change the simple broker simply removed subscriptions
upon receiving a DISCONNECT message assuming it was a result of
a client STOMP WebSocket session ending.

However, if the server-side application sends a DISCONNECT to
the broker in order to terminate a session, the STOMP WebSocket
session could remain unware without any further action. This
change ensures the simple broker sends a DISCONNECT_ACK message
downstream whenever it receives a DISCONNECT.

Issue: SPR-12288

This change adds a ChannelInterceptor that flips the immutable flag on
messages being sent. This allows components sending messages to leave
the message mutable for interceptors to further apply modifications
before the message is sent (and exposed to concurrency).

The interceptor is automatically added with the STOMP/WebSocket Java
and XML config and the StompSubProtocolHandler leaves parsed incoming
messages mutable so they can be further modified before being sent.

Issue: SPR-12321

AbstractMessageChannel triggers afterSendCompletion with previously resolved non-null Message in case of preSend returning null

Issue: SPR-12295

Issue: Issue: SPR-12272

 - clean up warnings
 - simplify ApplicationContext configuration

Issue: SPR-12272

Issue: SPR-12272

Consolidate inner classes used to invoke a subscriber with
interceptors.

Issue: SPR-12218