Prior to this commit, exceptions thrown while closing an InputStream in
AbstractResource were silently ignored.

This commit improves diagnostics for such failure scenarios by logging
the exception at DEBUG level.

Closes gh-23116

Update `FormatterRegistry` with `addPrinter` and `addParser` methods
that can be used to register Printer or Parser implementations in a
similar way to the existing `addFormatter` method.

Closes gh-23110

See gh-23052

Closes gh-23111

Closes gh-23064

Closes gh-23063

Closes gh-22957

Closes gh-22939

Closes gh-22242

Includes upgrade to Reactor Californium SR9 proper.

Closes gh-23091

Closes gh-23032

Closes gh-22981

Upgrade to Tomcat 9.0.21, Undertow 2.0.21, RxJava 2.2.9, Checkstyle 8.21, Mockito 2.28.2, Hibernate ORM 5.4.3

Centralizes rsocketVersion declaration in build.gradle; also includes upgrade to Reactor Dysprosium M2 proper.

See gh-23052

See gh-22383

Closes gh-22383

Closes gh-23052

See gh-23076

See gh-23076

See gh-23002

See gh-23002

Closes gh-23002

See gh-23073

This commit improves FreeMarkerConfigurerTests in spring-webmvc by
testing against FreeMarkerConfigurer instead of
FreeMarkerConfigurationFactoryBean and moves the original
FreeMarkerConfigurationFactoryBeanTests to spring-context-support in
the org.springframework.ui.freemarker package.

Closes gh-23073