Protect against NPE when escaping LiveBeansView

Issue: SPR-12252
Update default SockJS CDN location

This commit updates the default location of the SockJS' client library.
The previous location is being retired by the project maintainers.

The new default location is backed by several CDN providers:
* https://cdn.jsdelivr.net/sockjs/0.3.4/sockjs.min.js

See sockjs/sockjs-client#198

Issue: SPR-12254
Polishing
DefaultLobCreator supports JDBC 4.0 set-stream variants without length parameter

Issue: SPR-12265
DefaultLobCreator's streamAsLob mode supports JDBC 4.0 setBlob/Clob variants without length parameter as well

Issue: SPR-12265
StatementCreatorUtils uses setClob/setNClob with stream argument in case of typed String value exceeding 4000 characters (for Oracle compatibility)

Issue: SPR-12240
Polish Javadoc for @JmsListener
Polish Javadoc for BackOff implementations
Restore sleep interval between recovery attempt

Commit 6a04831 introduced a regression that lead to burst recovery
attempts when the broker is up but the listener is failing for some
reason (the most obvious one being that the destination does not
exist).

Since the sleep period between recovery attempts strategy is more
complex, we can't just sleep for a period of time. But we can create
an execution and apply it once which should work just fine for most
use cases.

Issue: SPR-12183
MethodReference accesses cached executor in a thread-safe manner

Issue: SPR-12269
Polishing
FormHttpMessageConverter uses a delegate class for JavaMail-based MIME encoding (isolating the JavaMail API dependency)

Issue: SPR-12108
JsonViewResponseBodyAdvice throws IllegalArgumentException in case of >1 view class specified

Issue: SPR-12270
Update default view resolver in MVC Java config

When not ViewResolver's have been registered, detect if the context
contains any other ViewResolver beans. If not, add InternalResourceVR
to match default DispatcherServlet behavior.

Issue: SPR-12267
Polishing
Correct check for ViewResolver beans

Check for bean names of type rather than actual beans.

Issue: SPR-12267
Polish ExecutorSubscribableChannel

Consolidate inner classes used to invoke a subscriber with
interceptors.
Add MessageHandlingRunnable

Issue: SPR-12272
Allow configuring custom ThreadPoolTaskExecutor

Issue: SPR-12272
Create a builder for Jackson ObjectMapper

Jackson2ObjectMapperBuilder now allows to create ObjectMapper and XmlMapper
instances easily thanks to its fluent API.

This builder is used in Jackson message converters and views to instantiate default
ObjectMapper and XmlMapper.

This commit also add a createXmlMapper property to
Jackson2ObjectMapperFactoryBean in order to allow to create easily a XmlMapper
instance.

Issue: SPR-12243