Set virtualHost on StompBrokerRelayRegistration

Prior to this commit, one couldn't set the virtualHost property on
StompBrokerRelayMessageHandler via JavaConfig, since
StompBrokerRelayRegistration's API didn't offer that possibility.

This commit adds a new method in StompBrokerRelayRegistration's fluent
API to set the virtualHost used by StompBrokerRelayMessageHandler.
Note: this property is already configurable via xml config.

Issue: SPR-11433
Add PropertyNamingStrategy field to ObjectMapperFB

Issue: SPR-11431
Fix typo in AbstractDelegatingSmartContextLoader
Fix memory leak in ConcurrentReferenceHashMap

Update ConcurrentReferenceHashMap to protect against references that
have been garbage collected but for some reason do not appear as a
`pollForPurge` result.

Also added purgeUnreferencedEntries() method to allow for programmatic
cleanup.

Issue: SPR-11440
Regularly purge ResolvableType cache

Update ResolvableType to call `purgeUnreferencedEntries` on the cache
on each get.

Issue: SPR-11394
Additional caching for ResolvableTypes

Add additional caching to ResolvableTypes and SerializableTypeWrapper
in order to improve SpEL performance.

Issue: SPR-11388
Add processExternalEntities support to OXM

Update OXM AbstractMarshaller to support processing of external
XML entities. By default external entities will not be processed.

Issue: SPR-11376
Next development version
Fix unused import warning
Fix minor error in AnnotationUtilsTests

TransactionalAndOrderedClass now extends TransactionalClass.

The tests passed anyway, but they did not actually verify what was meant
to be verified.
Support nested meta-annotations in AnnotationUtils

Prior to this commit, AnnotationUtils.findAnnotation(Class, Class)
claimed to recursively search through annotations; however, only one
level of annotations was supported by the algorithm.

This commit alters the search algorithm so that nested meta-annotations
(i.e., meta-annotations on meta-annotations) are also supported.

Issue: SPR-11448