Prior to this change, RestTemplate returned an empty response body if:

* HTTP return status 204 or 304
* Content-length header equals 0

This change adds a new condition for this, better supporting RFC7230
section 3.4, for connections that are closed without response body:

* No Content-length header
* No Transfer-encoding: chunked header value
* a Connection: close header value

See SPR-7911 for previous efforts in that space.

Issue: SPR-8016

Fixed the output stream incomplete data by explicitly flushing the OutputStreamWriter

Revised ControllerAdvice basePackages handling (based on package names instead of java.lang.Package)

Issue: SPR-12506

Issue: SPR-12500

Issue: SPR-12502

Fix for NPE when creating ProtobufHttpMessageConverter without ExtensionRegistryInitializer

Issue: SPR-12500

* SPR-12447:
  Add @AjSuppressWarnings on static mocks

Issue: SPR-12447

With this commit, Jackson builder is now used in spring-websocket
to create the ObjectMapper instance.

It is not possible to use the builder for spring-messaging
and spring-jms since these modules don't have a dependency on
spring-web, thus they now just customize the same features:
 - MapperFeature#DEFAULT_VIEW_INCLUSION is disabled
 - DeserializationFeature#FAIL_ON_UNKNOWN_PROPERTIES is disabled

Issue: SPR-12293

Add a protected getFlattenedMap method to the YamlProcessor that
subclasses can use to flatten a source Map so that it has the same
entries as the Properties, but retains order.

Issue: SPR-12499

FormHttpMessageConverter incorrectly determines that the media type
"multipart/form-data; charset=utf-8" is not multipart. This commit
allows the media type to contain a charset parameter.

Issue: SPR-10655

Issue: SPR-12479

Issue: SPR-12497

Issue: SPR-12493

Previously, any @Configuration class was enhanced to namely implement
DisposableBean in order to remove static callbacks that were registered
for that class. This leads to problem if an ApplicationContext is created
and destroyed within the lifecycle on another ApplicationContext in the
same class loader.

It turns out that the destruction callback is no longer necessary as the
interceptors are now stateless: the VM is free to reclaim any of those if
necessary.

Issue: SPR-12445

Issue: SPR-12488

Issue: SPR-12488

Issue: SPR-12486

Issue: SPR-12489

Issue: SPR-12487

Issue: SPR-12484

Issue: SPR-12483

Issue: SPR-12483

Issue: SPR-12483

Issue: SPR-12477

Issue: SPR-12476