When a request that accepts text/plain is received, the threaddump
endpoint will now return a thread dump in plain text. The format of
this text is modelled after the output produced by JVisualVM when
connecting to a remote process over JMX. Note that this output does
not include all of the information in, for example, JStack's output
as it is not available via Java 8's ThreadInfo API.

Rather than the custom formatting logic, using ThreadInfo's toString()
method was considered but its output is documented as being undefined
and implementation specific. The implementation used while developing
this feature produced output that did not match that of JStack or
JVisualVM and truncated stack traces quite considerably.

At the time of writing the format produced by the endpoint could be
consumed by both Thread Dump Analyzer [1] and https://fastthread.io.

Closes gh-2339

[1] https://github.com/irockel/tda

Apply checkstyle rule to ensure that private and package private
classes do not have unnecessary public methods. Test classes have
also been unified as much as possible to use default scoped
inner-classes.

Closes gh-7316

Closes gh-17393

See gh-17393

Closes gh-17409

Previously, the context path was set to an empty string. The led to
Jetty logging a warning about an empty context path and then using
/ instead.

This commit avoids the warning while leaving the context path's end
result unchanged by setting the context path to /.

Closes gh-17399

Closes gh-17404

See gh-17107

Closes gh-17408

Closes gh-17407

Closes gh-17406

Closes gh-17405

Closes gh-17404

Closes gh-17403

Closes gh-17402

Closes gh-17333

Closes gh-17401

This commit adds dependency management for Infinispan's Spring 5
modules that are introduced in 9.4.9.Final. It also removes redundant
exclusions for the dependency management for its Spring 4 modules.

Closes gh-17346

* gh-17278:
  Start building against Spring Session Corn-M3 snapshots

Closes gh-17278
See gh-17348

See gh-17278

See gh-17347

See gh-17349

See gh-17350

Closes gh-17385

Rename `StringToEnumIgnoringCaseConverterFactory` to
`LenientStringToEnumConverterFactory` and extended it to support
binding of YAML style 'true'/'false' values to 'ON'/'OFF'.

Closes gh-17385

Closes gh-17396

Update `StringToEnumIgnoringCaseConverterFactory` so that the
`getLettersAndDigits` method correctly appends `char` elements
rather than `int` elements.

Closes gh-17327

Closes gh-17394

See gh-12005

See gh-12005

See gh-17387

Closes gh-17387

Escape lines that look like variable references but should actually be
included verbatim.

Closes gh-17386

See gh-12005

Since to no longer use docbook, we can't use `partintro`.

See gh-12005

Closes gh-17387

Escape lines that look like variable references but should actually be
included verbatim.

Closes gh-17386

* gh-16447:
  Avoid bindable properties check when target has null value

Closes gh-16447

See gh-16447

* gh-17271:
  Remove redundant invocation of getActiveProfiles

Closes gh-17271