Closes gh-12620

Closes gh-12619

Closes gh-12618

Closes gh-12617

Closes gh-12616

Closes gh-12615

Closes gh-12614

Closes gh-12613

Closes gh-12573

* gh-12554:
  Polish "Use this.out in SummaryProgressReporter.finished()"
  Use this.out in SummaryProgressReporter.finished()

See gh-12554

Closes gh-12554

Closes gh-1778

* pr/12555:
  Rename expose to include

Closes gh-12555

* pr/12553:
  Polish

Closes gh-12553

* pr/12491:
  Add OAuth2 server implementation section to docs

As auto-configuration for Spring Security OAuth has been removed
from Spring Boot 2.0 and Spring Security 5 doesn't have OAuth
2.0 Authorization / Resource Server support yet, it has not
been obvious at all how to implement an OAUth 2.0 server with
Spring Boot 2.0.

For that reason, this new section briefly explains the current
temporary situation and points to the spring-security-oauth2-autoconfigure
module that restores the auto-configuration support for OAuth
2.0 Authorization and Resource Servers.

Closes gh-12491

* pr/12528:
  Polish "Iterate map by using lambda function"
  Iterate map by using lambda function

See gh-12528

Closes gh-12528

Change `ConfigurationPropertySource.containsDescendantOf` to have a
default implementation that return `UNKNOWN`.

Fixes gh-12539

Fixes gh-12540

Update `Map` and `Collection` binders to create a copy of the existing
collection whenever possible. Prior to this commit the binder would
always mutate the existing value and then call the setter with the
same instance. This could cause issues if the setter expected a
different instance.

Fixes gh-12322

Ensure that JSON response is returned when extracting data from the
error details.

See gh-12513

* gh-12527:
  Polish "Follow project convention for lambda expression"
  Follow project convention for lambda expression

Csee gh-12527

Closes gh-12527

Closes gh-12529

Refine `BasicErrorController` mappings so that only JSON and XML get
structured responses. A simple string response is returned for all
other media types.

Fixes gh-12513