As of Spring Framework 5.1, we're depending on the Reactor Californium
release train.
Reactor Netty is now at version 0.8 and changed its artifact
coordinates, package names and broke several APIs. Spring Framework is
now up-to-date with those changes and this commit does the same for
Spring Boot.

Note that in that process, the `NettyServerCustomizer` has been changed
since the former `HttpServerOptions.Builder` API is now gone from
Reactor Netty, and we're now relying on immutable server instances
instead of a stateful builder pattern.

See gh-13321

Closes gh-13359

Closes gh-12631

Closes gh-12687

* pr/13351:
  Add "Managed dependency upgrade" section

Closes gh-13351

Closes gh-13152

* pr/13331:
  Auto-configure jOOQ with TransactionListenerProvider

Closes gh-13331

Closes gh-13122

Closes gh-13357

Previously, WebMvcTags would fall back to using the request’s path
info if Spring MVC’s best matching path pattern attribute was not
available. For non-Spring MVC web frameworks that support path
variables, such as Jersey, this led to an explosion of URI tags that
could exhaust the heap.

Closes gh-12447

See gh-13353

See gh-13352

* pr/13338:
  Polish "Retrieve javax.cache.CacheManager using Bean ClassLoader"
  Retrieve javax.cache.CacheManager using Bean ClassLoader

Closes gh-13338

This commit uses the bean's classloader to retrieve the CacheManager to
prevent issues with off-heap serialization.

See gh-13338

* pr/12707:
  Polish "Add auto-configuration for WebServiceTemplate"
  Extract ClientHttpRequestFactory detection to its own class
  Add auto-configuration for WebServiceTemplate

Closes gh-1270

See gh-12707

See gh-12707

* pr/13345:
  Remove usage of deprecated Matchers class

Closes gh-13345

* pr/13343:
  Polish stream creation in some PropertySources

Closes gh-13343