ClassReader relies on autoboxing for reuse of cached primitive values

Issue: SPR-12365
HibernateTransactionManager supports result access after completion

Issue: SPR-12349
Support text/xml and application/*+xml in Jackson XML message converter

Issue: SPR-12366
TilesConfigurer defensively expects null from getResources in case of no resources found

Also includes order preservation for resource results with Tiles 2 as well as retrieval failure logging with Tiles 3.

Issue: SPR-12362
Polishing
Add author attribution for htmlEscape methods

Issue: SPR-9293
Add ImmutableMessageChannelInterceptor

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
Add mention of java.util.Optional in @MVC

Issue: SPR-12370