Issue: SPR-14960

Issue: SPR-14958

Issue: SPR-12889

Issue: SPR-14926
Issue: SPR-12926

* getBeanDefinitionNames defensively returns a copy of the bean definition names array.
* copyConfigurationFrom provides an independent AutowireCandidateResolver instance and copies a ConversionService and dependency comparator configuration as well.
* findAutowireCandidates only considers a self reference fallback for direct dependency declarations, not as a collection element.

Issue: SPR-14897
Issue: SPR-14921
Issue: SPR-14965

Issue: SPR-14924

In general, web.util is supposed to remain lowest-level, not depending on any other web.* package. Since web.client also has a support package, a corresponding web.server.support package seemed appropriate for a helper class depending on ServerWebExchange in web.server itself.

The ResponseStatusException is now also supported in Spring MVC
through the ResponseStatusExceptionResolver.

Issue: SPR-14895

The recent refactoring lead to
java.lang.NoClassDefFoundError: io/reactivex/Completable

where only RxJava 1 is in the classpath. Most likely due to the
lack of prefix in Completable::complete with rx package to avoid
the RxJava 2 reference.

Issue: SPR-13481

Issue: SPR-13188

Reactor Netty's `HttpServerResponse` has a new `sendFile` signature that
takes a `Path` instead of a `File`.

Issue: SPR-14916

Issue: SPR-14939

Issue: SPR-14937

Main differences with the Spring MVC original implementation:
 - Default redirect HTTP code is 303 See Other since we can assume
   all HTTP clients support HTTP 1.1 in 2016
 - No more http10Compatible property, use statusCode instead
 - By default the redirect is relative to the context path
 - A builder allow to set various properties if needed
 - In UrlBasedViewResolver, a Function<String, RedirectView>
   redirectViewProvider property allows to customize RedirectView
   instances in a flexible way

Issue: SPR-14534

Simplify getAdapterFrom/To into a single getAdapter method that looks
for an exact match by type first and then isAssignableFrom.

Also expose shortcut methods in ReactiveAdapter to minimize the need
for access to the ReactiveTypeDescriptor.

Issue: SPR-14902

The ReactiveAdapterRegistry now detects the presence of Reactor. In
practice Reactor is required for the Spring Framework reactive support
and it is expected to be present.

The registry however is now capable of being neutral if Reactor is not
present on the classpath for example where other Spring projects may
not have the same assumptions about Reactor's presence.

Issue: SPR-14902

Collapse ReactiveAdapter hierarchy into a single class that simply
delegates to functions for converting to/from a Publisher.

A private ReactorAdapter extension automaticlaly wraps adapted,  "raw"
Publisher's as Flux or Mono depending on the semantics of the target
reactive type.

Issue: SPR-14902

Issue: SPR-14902

ReactiveTypeDescriptor is now a top-level type with named constructors.
It also contains and provides a getter for the actual type.

Issue: SPR-14902

Issue: SPR-14952

This commit polishes previous one by also accepting
generic types explicitly declared with a class that
extends DataBuffer allowing to write Flux<DefaultDataBuffer>
for example.

Issue: SPR-14952

This modifies the signature of
ReactiveHttpOutputMessage#writeAndFlush(...) in order to
be able to use Flux<Flux<DataBuffer>> objects as arguments of
this method.

Issue: SPR-14952

This commit polishes Kotlin nullable support by reusing
MethodParameter#isOptional() instead of adding a new
MethodParameter#isNullable() method, adds
Kotlin tests and introduces Spring Web Reactive
support.

Issue: SPR-14165

Where `isOptional` is used, also check for `isNullable` i.e.
values are not considered required if they are Kotlin nullables:
- spring-messaging: named value method arguments
- spring-web: named value method arguments
- spring-webmvc: request parts

This means that Kotlin client code no longer has to explicity specify
"required=false" for Kotlin nullables -- this information is inferred
automatically by the framework.

Issue: SPR-14165

Added a BodyExtractor for Flux<DataBuffer>, and a BodyInserter for
Publisher<DataBuffer>

Issue: SPR-14918

Issue: SPR-14467

Issue: SPR-14948

* SPR-14941:
  Fix NPE in ServletServerHttpResponse.ResponseBodyProcessor.write

Issue: SPR-14941

Issue: SPR-14942

In case the filter is also registered to the ERROR dispatcher, the
following happens:
* the filter is executed once for the regular execution
* the filter should be executed a second time when dispatched to error

Since the filter is a `OncePerRequestFilter`, the filter is only
executed once and won't be executed when handling the error.

This can lead to situations like spring-projects/spring-boot#7348

This commit makes this filter a simple `GenericFilterBean`.

Issue: SPR-14891