This commit adds an assertion to DefaultTestContext's
getApplicationContext() method to ensure that a context loaded by the
Spring TestContext Framework (TCF) or retrieved from the ContextCache
is still active. This extra check helps to avoid situations where
developers manually close a cached context instead of relying on the
@DirtiesContext support.

Issue: SPR-12932

The changes made in 0cb22fc8 would
result in contexts not being properly closed if evicted from the
ConcurrentReferenceHashMap by the Garbage Collector.

This commit reverts those changes and returns to using standard
ConcurrentHashMaps for the time being.

Issue: SPR-7687

Issue: SPR-12683

Improve extensibility of TestContext bootstrapping & context caching

These commits include numerous refactorings and enhancements to the
bootstrapping and context caching mechanisms in the Spring TestContext
Framework.

Issue: SPR-12683

 - DefaultBootstrapContext and DefaultCacheAwareContextLoaderDelegate
   are now public classes in the 'support' subpackage.

 - Introduced getCacheAwareContextLoaderDelegate() in
   AbstractTestContextBootstrapper as an extension point for configuring
   custom ContextCache support.

 - Introduced reflection-based createBootstrapContext() utility method
   in BootstrapUtils; TestContextManager now delegates to BootstrapUtils
   in order to avoid package cycles.

 - Introduced logStatistics() method in the ContextCache API and defined
   statistics logging category as a constant.

 - DefaultCacheAwareContextLoaderDelegate now delegates to
   ContextCache.logStatistics().

Issue: SPR-12683

 - ContextCache is now a public interface.

 - Introduced public DefaultContextCache implementation in the 'support'
   subpackage.

Issue: SPR-12683

Issue: SPR-12683

This commit moves the responsibility of building a TestContext from the
TestContextManager to a TestContextBootstrapper.

In addition, DefaultTestContext is now a public class residing in the
"support" subpackage.

Issue: SPR-12683

Issue: SPR-12683

Prior to this commit, the ContextCache in the Spring TestContext
Framework (TCF) cached ApplicationContexts in a ConcurrentHashMap using
strong references. This practice can occasionally lead to
OutOfMemoryErrors when running a large number of tests in a test suite
with varying context configuration since the context cache becomes
overpopulated over time.

This commit addresses this issue by using Spring's
ConcurrentReferenceHashMap which uses SoftReferences for both the keys
(i.e., MergedContextConfiguration instances) and values (i.e.,
ApplicationContexts) stored in the map that backs the ContextCache.

Issue: SPR-7687

This change adds support for broadcasting messages with unresolved
user destinations so that other servers can try to resolve it.
That enables sending messages to users who may be connected to a
different server.

Issue: SPR-11620

Issue: SPR-11620

Prior to this commit, ClassLevelDirtiesContextTests existed for
verifying the expected behavior of @DirtiesContext declared at the
class level in conjunction with JUnit and SpringJUnit4ClassRunner.

This commit introduces analogous tests for TestNG in the new
ClassLevelDirtiesContextTestNGTests class.

Furthermore, ContextCacheTestUtils and TrackingTestNGTestListener have
been introduced to reduce code duplication across the test suite.

Issue: SPR-12918

Issue: SPR-11841

Issue: SPR-12890

Issue: SPR-12925

The attributes of @JmsListener allows to specify the reference to a key
in the Environment but @SendTo did not.

This commit fixes this inconsistency so that response destinations are
now also externally configurable.

Issue: SPR-12899

AbstractApplicationContext collects early ApplicationEvents and publishes them once the multicaster is available

Issue: SPR-12902

Issue: SPR-12900

Issue: SPR-12905

Previously, the "pubSubDomain" drove the resolution of both the
destination of the listener and the default response destination.

A new "replyPubSubDomain" attribute has been added on the base listener
and  can be used to listen on a topic and reply to a queue (or vice
versa). The attribute is exposed via the "response-destination-type" XML
attribute on the listener container element. It is also available on the
JmsListenerContainerFactory for use with the @JmsListener infrastructure.

Issue: SPR-12911

Issue: SPR-12905

Issue: SPR-12915

Issue: SPR-12910

Issue: SPR-12895

This commit increases the extensibility of
AbstractTestContextBootstrapper by making the resolveContextLoader()
and resolveExplicitContextLoaderClass() methods protected instead of
private.

Furthermore, resolveContextLoader() now throws an IllegalStateException
if getDefaultContextLoaderClass() returns null.

Issue: SPR-12682

This commit improves the documentation for ScriptUtils by explicitly
mentioning that a JDBC Connection supplied to the one of the
executeSqlScript() methods will not be released automatically.

Issue: SPR-12908