DefaultListableBeanFactory does not trigger early candidate creation ahead of primary bean selection

Issue: SPR-14611

Issue: SPR-14626

Issue: SPR-14625

Issue: SPR-14624

Issue: SPR-14609
(cherry picked from commit ab686732)

Issue: SPR-14609

Issue: SPR-7549

Includes optimized method/header resolution in CorsConfiguration.

Issue: SPR-14617

Prior to this commit, extracting an HTTP response with an empty body
and no Content-Type header using the WebClient would:

* trigger the use of the Jackson2JsonDecoder
* throw a NoSuchElementException because of the use of `Flux.single()`

This commit changes this behavior to `Flux.singleOrEmpty()` to avoid
throwing exceptions for empty Flux instances.

Issue: SPR-14582

Issue: SPR-14607

Issue: SPR-14616

Default ClientOptions enable SSL support.

Issue: SPR-14593

* reactor-core 3.0.1.BUILD-SNAPSHOT
* reactor-netty 0.6.0.BUILD-SNAPSHOT

This commit ensures that JUnit XML reports are generated in the old
Gradle 2.x location for all tests in the spring-test module.

Issue: SPR-14569

Issue: SPR-14569

Since the upgrade to Gradle 3, our Bamboo build is failing because it
can't find test reports "at the usual location".

This commit restores the location that Gradle 2 was using until we
upgrade to a version of Bamboo that supports it.

Issue: SPR-14569

Fix the build to work with reactor-core-3.0.0.RELEASE

Previously the IDE (STS) was resolving a different reactor-core
version (3.0.0.BUILD-SNAPSHOT) than the build (3.0.0.RELEASE). This
discrepancy was due to the fact that reactor-netty now brings in
reactor-core 3.0.0.RELEASE. Gradle's version conflict resolution is to use
the latest version. However, the optional dependency on reactor-core
3.0.0.BUILD-SNAPSHOT was making the build path of the IDE use the SNAPSHOT.

This fix leverages a resolutionStrategy to ensure a consistent version of
reactor-core is used throughout the entire project. It also bumps up the
reactor-core version to 3.0.0.RELEASE to be consistent with reactor-netty.
Care is taken to only change 3.x vesion since 2.x is still used within
the codebase.

Issue: SPR-14594

Issue: SPR-14600

(cherry picked from commit 5222489a)

Issue: SPR-14599

Issue: SPR-14599

Issue: SPR-14585
(cherry picked from commit da567580)

Issue: SPR-14598
(cherry picked from commit 188e5327)

(cherry picked from commit 1932a9d7)

This commit adds a setter for the default persistence unit's
defaultPersistenceUnitRootLocation attribute.

Issue: SPR-14595

Issue: SPR-14580

Issue: SPR-14585

Issue: SPR-14585

Issue: SPR-11217

Since we have a dedicated section regarding Ehcache that is only
applicable to Ehcache 2.x, this commit clarifies that Ehcache 3.x is
JSR-107 compliant and the JCache support should be used with it
rather than attempting to configure the Ehcache 2.x support.

Commit 240f254b has introduced support for `java.util.Optional` in the
cache abstraction. If such type is present, the contained value is cached
if it is present.

This new feature slightly changed the semantic of `#result` that was
documented up till this commit as the "return value of the method
invocation". This is no longer true as `#result` for `Optional<T>`
refers to the `T` instance and not the `Optional` instance.

This commit clarifies both the javadoc and the documentation.

Issue: SPR-14587

* pr/1132:
  Add aditional example to CronSequenceGenerator