CachingDestinationResolverProxy for slow target DestinationResolvers

Issue: SPR-11939
Polishing

Issue: SPR-11939
Synchronize request init in AbstractHttpSockJsSession

Although unlikely in practice (but not impossible), the SockJS
integration tests write a message while the request is initializing.
This change adds synchronization around request intiailization
for the SockJS HTTP sesion.

Issue: SPR-11916
Log name of test for WebSocket integration tests

This makes it easier to trace log output on the CI server where the
output is per class.
Standard use of resolvedDestinationCache Map; fixed formatting

Issue: SPR-11939
Introduce programmatic tx mgmt in the TCF

Historically, Spring's JUnit 3.8 TestCase class hierarchy supported
programmatic transaction management of "test-managed transactions" via
the protected endTransaction() and startNewTransaction() methods in
AbstractTransactionalSpringContextTests.

The Spring TestContext Framework (TCF) was introduced in Spring 2.5 to
supersede the legacy JUnit 3.8 support classes; however, prior to this
commit the TCF has not provided support for programmatically starting
or stopping the test-managed transaction.

This commit introduces a TestTransaction class in the TCF that provides
static utility methods for programmatically interacting with
test-managed transactions. Specifically, the following features are
supported by TestTransaction and its collaborators.

 - End the current test-managed transaction.

 - Start a new test-managed transaction, using the default rollback
   semantics configured via @TransactionConfiguration and @Rollback.

 - Flag the current test-managed transaction to be committed.

 - Flag the current test-managed transaction to be rolled back.

Implementation Details:

 - TransactionContext is now a top-level, package private class.

 - The existing test transaction management logic has been extracted
   from TransactionalTestExecutionListener into TransactionContext.

 - The current TransactionContext is stored in a
   NamedInheritableThreadLocal that is managed by
   TransactionContextHolder.

 - TestTransaction defines the end-user API, interacting with the
   TransactionContextHolder behind the scenes.

 - TransactionalTestExecutionListener now delegates to
   TransactionContext completely for starting and ending transactions.

Issue: SPR-5079
Merge from sbrannen/SPR-5079

* SPR-5079:
  Introduce programmatic tx mgmt in the TCF
Introduce TestNG tests for programmatic tx mgmt in the TCF

Issue: SPR-5079