Dependency management for the `HikariCP-java6` dependency is no longer
needed since Java 6 is no longer supported by Spring Boot.

The HikariDriverConfigurationFailureAnalyzer has been updated with the
current message thrown by HikariCP in this failure scenario.

Closes gh-8147

Previously, TestRestTemplate applied the root URI to URIs by
converting them to a String and then passing the String to the
RestTemplate delegate. Being a String, meant that the URI passed
through RestTemplate's standard URI template expansion processing
using the configured UriTemplateHandler. While this caused the root
URI to be applied, it also had the unwanted side-effect of
encoding the URI for a second time.

This commit updates TestRestTemplate so that, when configured with a
RootUriTemplateHandler, it applies the root URI directly and then
passes a modified URI to the RestTemplate delegate. Being a URI means
that no template expansion is performed and the possible double
encoding is avoided.

Closes gh-8163

Closes gh-8182

See gh-8180

See gh-8179

See gh-8148

* pr/8148:
  Polish

Closes gh-8148

* pr/8161:
  Clear system property in SpringApplicationTests

See gh-8101
Closes gh-8161

* pr/8157:
  Polish contribution
  Update copyright header

Closes gh-8157

See gh-8157

Update `ConfigurationPropertiesBindingPostProcessor` to use a more
exhaustive hierarchy search when checking for `@Validated`.

Fixes gh-8150

Update `EndpointMBeanExporter` to ensure that `JmxEndpoint` as well
as regular `Endpoint` beans are considered when searching the parent
context.

Prior to this commit if the same `JmxEndpoint` was registered in the
both the child and parent context then the `context=` element of the
name wasn't added.

Fixes gh-8152

Since SPR-15196, the behavior of `Assert` methods changed and some were
deprecated. This commit adapts to the new error mechanism implemented in
`Assert.instanceOf`.

Fixes gh-8140

This commit updates the Spring Boot codebase to adapt to the removal of
`Assert.notNull(Object)` in SPR-15196.

See gh-8140

Closes gh-8077

* gh-7744:
  Make use of new extensions point in IntegrationComponentScanRegistrar

SI 5 has made IntegrationComponentScanRegistrar more extensible by
offering a method for getting the back packages that can be
overridden.

This commit takes advantage of that change by removing our creation
of "fake" annotation metadata and overriding getBackPackages to return
the auto-configuration packages instead.

Closes gh-7744

Closes gh-7557

Closes gh-8136

* gh-5344:
  Polish "Upgrade to Flyway 4.0"
  Upgrade to Flyway 4.0

See gh-5344

Closes gh-5344