Prior to this commit, the hasContributors() method incorrectly returned
false if contributors had been configured.

This commit fixes the logic in hasContributors() and documents it.

Closes #27271

Closes gh-27289

Potential fix for issue reported at
https://github.com/reactor/reactor-netty/issues/1746

Closes gh-27250

* pr/27260:
  Fix typo in DefaultPartHttpMessageReader

Closes gh-27260

See gh-27260

See gh-27250

* pr/27248:
  Polish contribution
  Polish tests

Closes gh-27248

See gh-27248

See gh-27248

Closes gh-27220

See gh-27220

* pr/27238:
  Polish printMvcResultsToWriterWithFailingGlobalResultMatcher()

Closes gh-27238

See gh-27238

See gh-27234

This commit simplifies getInternalBeanFactoryForBean() in
AbstractBeanFactoryBasedTargetSourceCreator via
Map::computeIfAbsent.

Closes gh-27234

To improve the developer experience and avoid the use of String
literals, this commit provides overloaded support via Charset for
character encoding in MockHttpServletRequestBuilder and
ContentResultMatchers.

Closes gh-27231

Commit e4b9b1fa introduced support for setting the default character
encoding in MockHttpServletResponse.

This commit introduces support for configuring the default character
encoding in the underlying MockHttpServletResponse used in MockMvc.

Closes gh-27230

Prior to this commit, MockMvc applied global ResultMatchers before
global ResultHandlers. This lead to unexpected scenarios where a
failing matcher would prevent a handler from being applied.

One concrete use case is `alwaysDo(print(System.err))` which should
print out MockMvc results for debugging purposes. However, if MockMvc is
configured with something like `alwaysExpect(content().string("?"))`
and the expectation fails, the user will never see the expected debug
output to help diagnose the problem.

This commit addresses this issue by applying global ResultHandlers
before ResultMatchers in MockMvc.

Closes gh-27225

Prior to this commit, it was possible to set the character encoding
in MockHttpServletResponse via setCharacterEncoding() or
setContentType(); however, those methods append "charset=..." to the
Content-Type header which may not be an acceptable side effect.

This commit addresses this shortcoming by introducing a new
setDefaultCharacterEncoding() in MockHttpServletResponse which allows
one to override the previously hard coded value of "ISO-8859-1". In
addition, setDefaultCharacterEncoding() does not modify the Content-Type
header.

The reset() method has also been updated to reset the character encoding
to the configured default character encoding.

Closes gh-27214

Closes gh-27203

Follow-up for commit bb816c12

See gh-27203

See gh-26493

Closes gh-27219

See gh-27223

Closes gh-27223

Closes gh-27218

Closes gh-27216

This commit improves the documentation for @Cacheable to point out that
`null` will be stored in the cache for an empty `Optional` return value.

Closes gh-27184

Prior to this commit, if the TaskExecutor configured in
WebSocketMessageBrokerStats for the inboundChannelExecutor or
outboundChannelExecutor was not a ThreadPoolTaskExecutor, a
StringIndexOutOfBoundsException was thrown when attempting to parse the
results of invoking toString() on the executor.

The reason is that ThreadPoolTaskExecutor delegates to a
ThreadPoolExecutor whose toString() implementation generates text
containing "pool size = ...", and WebSocketMessageBrokerStats'
getExecutorStatsInfo() method relied on the presence of "pool" in the
text returned from toString().

This commit fixes this bug by ensuring that the text returned from
toString() contains "pool" before parsing the text. If "pool" is not
present in the text, getExecutorStatsInfo() now returns "unknown"
instead of throwing a StringIndexOutOfBoundsException.

Closes gh-27209

Closes gh-26631

Closes gh-27204