xmlunit 2.1.0 is the latest release for xmlunit.
Most of the xmlunit functionality used within spring-framework
was done through the xmlunit 1.x helper class
`org.custommonkey.xmlunit.XMLAssert`.

As of xmlunit 2.0.0 most of the XML comparison methods are done
through hamcrest matchers exposed by the xmlunit-matchers
library. In some cases during the migration, the matchers
had to be customized with custom `NodeMatcher` or
`DifferenceEvaluator` instances in order to keep the assertions
correct (they were performed with xmlunit 1.x previously).

Issue: SPR-14043

This commit adds support for Google Protobuf 3.0.0 and make some changes
in the additional formats support:
* "com.googlecode.protobuf-java-format:protobuf-java-format" is no
longer required and its required version has been raised to 1.3+
(this lib adds support for JSON, XML, HTML formats)
* "com.google.protobuf:protobuf-java-util" is also now supported for
JSON format

Issue: SPR-13589

Issue: SPR-13344

Issue: SPR-14467

 - Added Woodstox before Aalto in the spring-web build, so that Woodstox
   is used as StAX implementation, and not the less featured Aalto.
 - Hardcoded Aalto dependency in XmlEventDecoder, instead of relying on
   the StAX XMLInputFactory.

Issue: SPR-14431

This commit removes `GuavaCache` and support classes. Caffeine supersedes
the caching support in the Google Guava library with an actively maintained
Java 8+ version in standalone form.

As it is the only Guava feature Spring framework integrates with, this
commit removes effectively any reference to Guava.

Issue: SPR-13797

Issue: SPR-13575

Issue: SPR-13294

Issue: SPR-13793

This commit also renames WebSocketIntegrationTests to WebSocketHandshakeTests.

Issue: SPR-14328

This commit adds a test runtime dependency on log4j 2 for every project
and migrates all log4j.properties files to log4j2-test.xml files.

Issue: SPR-14431

Issue: SPR-14429

This commit also removes outdated support classes for Oracle, GlassFish, JBoss.

Issue: SPR-14429

Commit 09008088 resolved the previous issue by moving the warning
suppression from the method parameter to the method itself.

Issue: SPR-13188

This commit also fixes broken javadoc links and code references.

Issue: SPR-13188

This commit introduces initial support for JUnit Jupiter (i.e., the new
programming and extension models in JUnit 5) in the Spring TestContext
Framework.

Specifically, this commit introduces the following.

- SpringExtension: an implementation of multiple extension APIs from
  JUnit Jupiter that provides full support for the existing feature set
  of the Spring TestContext Framework. This support is enabled via
  @ExtendWith(SpringExtension.class).

- @SpringJUnitConfig: a composed annotation that combines
  @ExtendWith(SpringExtension.class) from JUnit Jupiter with
  @ContextConfiguration from the Spring TestContext Framework.

- @SpringJUnitWebConfig: a composed annotation that combines
  @ExtendWith(SpringExtension.class) from JUnit Jupiter with
  @ContextConfiguration and @WebAppConfiguration from the Spring
  TestContext Framework.

Issue: SPR-13575

Issue: SPR-13188

Issue: SPR-14362

Latest dependency updates (HttpAsyncClient 4.1.2, HtmlUnit 2.22, Selenium 2.53.1, JOpt Simple 5.0.2)

Issue: SPR-14327

Issue: SPR-14385

Prior to this commit, any attempt to include a bean of type
ServletServerContainerFactoryBean in the WebApplicationContext for an
integration test class annotated with @WebAppConfiguration in
conjunction the Spring TestContext Framework (TCF) would have resulted
in an IllegalStateException stating that "A ServletContext is required
to access the javax.websocket.server.ServerContainer instance."

In such scenarios, the MockServletContext was in fact present in the
WebApplicationContext; however there was no WebSocket ServerContainer
stored in the ServletContext.

This commit addresses this issue by introducing the following.

- MockServerContainer: a private mock implementation of the
  javax.websocket.server.ServerContainer interface.

- MockServerContainerContextCustomizer: a ContextCustomizer that
  instantiates a new MockServerContainer and stores it in the
  ServletContext under the attribute named
  "javax.websocket.server.ServerContainer".

- MockServerContainerContextCustomizerFactory: a
  ContextCustomizerFactory which creates a
  MockServerContainerContextCustomizer if WebSocket support is present
  in the classpath and the test class is annotated with
  @WebAppConfiguration. This factory is registered by default via the
  spring.factories mechanism.

Issue: SPR-14367

Issue: SPR-14328

Issue: SPR-14385