Closes gh-11416

HiddenHttpMethodFilter can be problematic as it causes early
consumption of a request body if the body may contain parameters. This
happens as the filter needs to read the parameters to see if an
_method parameter is present. The filter is only beneficial for web
applications that are the hidden HTTP method functionality but is
potentially detriimental to all applications that are not. As such
we no longer believe that it should be enabled by default and users
should be required to opt in.

Closes gh-16953

Closes gh-17432

Previously, if a user defined a MongoDbFactory bean but did not define
a client bean, MongoDataAutoConfiguration would back off leaving the
context without a MongoTemplate, etc.

This commit reworks the auto-configuration so that only the
auto-configuration of a MongoDbFactory is dependent on the existence
of a Mongo client bean. Auto-configuration of the other components
that depend on a MongoDbFactory will now continue in the absence of a
Mongo client bean.

Closes gh-17416

* gh-17412:
  Polish "Use Spring 5 module of Jersey"
  Use Spring 5 module of Jersey

Closes gh-17412

See gh-17412

See gh-17412

* gh-17411:
  Polish "Polish GradleCompatibilityExtension's javadoc"
  Polish GradleCompatibilityExtension's javadoc

Closes gh-17411

See gh-17411

See gh-17411

Closes gh-17429

Closes gh-17428

Update `ValidationBindHandler` so that a custom `AbstractBindingResult`
is used rather than `BeanPropertyBindingResult`. This allows us to
validate results, regardless of whether the actual bound instance has
public getters or setter.

Closes gh-17424

* pr/17356:
  Polish "Allow Undertow's options to be configured via the environment
  Allow Undertow's options to be configured via the environment

Closes gh-17356

See gh-17356

See gh-17356

* pr/17418:
  Polish "Provide links / when using a separate management port"
  Provide links for actuators at / when using a separate management port

Closes gh-17418

See gh-17418

See gh-17418

Closes gh-17422

Update `ValidationBindHandler` so that any non-null result returned by
the parent `onFailure` method triggers re-validation.

Fixes gh-17421

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