Issue: SPR-17155

Prior to this commit, an bug introduced in SPR-16949 prevented
`Mono.empty` bodies from being written to the response.

This commit ensures that empty bodies still trigger the writing to the
response and does not hang the processing of the exchange.

Issue: SPR-17220

In order to prevent instantiation of utility classes, this commit
makes NamedParameterBatchUpdateUtils `abstract`.

Issue: SPR-17215

Issue: SPR-17215

Issue: SPR-17209

Issue: SPR-17137

This commit represents a best effort attempt at fixing remaining
"a" vs. "an" grammatical errors related links specified via a fully
qualified class name.

Issue: SPR-17208

This reverts commit 253ffd71.

Issue: SPR-17208

Since the `initStrategies` method is there to be extended, the related
attributes should be `protected` as well.

I edited for spelling, punctuation, grammar, usage, and corporate voice. I also added cross-references and links to the Javadoc in a number of places.

* pr/1938:
  Polish

Closes gh-1938

Issue: SPR-17090

Issue: SPR-17198

When used as global Netty resources, ReactorResourceFactory creates and
sets those resources on Reactor's HttpResources directly.

When that ReactorResourceFactory bean is destroyed, those resources are
disposed but HttpResources still holds a reference to those and may try
to use them again.

This commit uses HttpResources to clear those resources and its
references to it, when the ReactorResourceFactory is treating those as
global.

Issue: SPR-17199

* pr/1934:
  Fix usage of deprecated functionality in docs

Closes gh-1934

Issue: SPR-17174

Issue: SPR-17160

Includes XMLUnit 2.6.1 and Undertow 2.0.13.

Issue: SPR-16115

Issue: SPR-17191

This reverts commit 29ce6685.

Issue: SPR-17179

Issue: SPR-17174

JettyResourceFactory, similar to ReactorResourceFactory, allows
to share resources (Executor, ByteBufferPool, Scheduler) between
Jetty clients and servers.

Issue: SPR-17179

Issue: SPR-17189

Includes upgrade to Hibernate ORM 5.3.5, EclipseLink 2.7.3, Selenium HtmlUnit Driver 2.32.1, Jetty 9.4.12 RC2.