Issue: SPR-16075

Issue: SPR-16073

Issue: SPR-16066

Issue: SPR-16059

Issue: SPR-16066

Includes redeclaration of CodecConfigurer.DefaultCodecs without concrete Jackson decoder/encoder references in order to avoid hard Jackson dependency.

Issue: SPR-16064

Before this commit, when adding filters to a builder obtained via
`WebClient.mutate()`, the filters were added both to the original client
as well as the mutated builder. This commit fixes that.

Issue: SPR-16059

Issue: SPR-16055

Issue: SPR-16063

Properly separate tocbot from asciidoctor styles and use main.css to
include both.

Prior to this commit, the `ResourceWebHandler` would itself handle the
response with an HTTP 404 in many cases, including a missing static
resource.

This does not give a chance to `WebExceptionHandler` instances to handle
that error and, for example, display an error page.

See spring-projects/spring-boot#8625

Issue: SPR-16023

Prior to this commit, the Resource `HandlerMapping` configured by
`@EnableSpringMvc` would be set up with only one custom
`HandlerInterceptor` (the one exposing the `ResourceUrlProvider` for
resolving URLs of static resources).

This behavior is not consistent with the rest of the default
configuration which leverages the interceptors configured against the
interceptor registry (with possible user-provided ones).

This change allows to register interceptors against resource handling;
this can be useful for metrics purposes, as in
spring-projects/spring-boot#10335.

Issue: SPR-16034

Easier to find (at the top level) and better summary of testing support.
Improve structure headings names.
Remove or update outdated content.

Issue: SPR-14579

Issue: SPR-16043

Issue: SPR-16054

Optimized for viewing in left TOC.

* pr/1549:
  Fix doc format

Closes gh-1549

The Javadoc on tag classes now has all the information including a
list of all tags at the package level, HTML tables listing tag
attributes in each tag class, and class level description that is
as good or in many cases better than what was in the reference.

Issue: SPR-16045

1. Move schemas to local appendix within each top-level section.
2. Link to Javadoc for JSP tags
3. Purge Class Spring usage information

Issue: SPR-16045

The WebTestClient now takes advantage of the support for decoding
response to Void.class in WebClient so that applications can use
expectBody(Void.class) to the same effect as using
response.bodyToMono(Void.class) as documneted on WebClient#exchange.

The top-level, no-arg returnResult method (added very recently) has been
retracted, since the use of returnResult at that level, i.e. without
consuming the response content, should be used mainly for streaming.
It shouldn't be used for "no content" scenarios.

Documentation and Javadoc have been udpated accordingly.