Issue: SPR-17129

This commit makes sure that in DataBufferUtils.write, any received data
buffers are returned as part of the returned flux, even when an error
occurs or is received.

Issue: SPR-16782

Issue: SPR-17267

Issue: SPR-17261

Issue: SPR-17256

Issue: SPR-17256

Also includes Apache Johnzon 1.1.9.

Issue: SPR-17255

`ForwardedHeaderFilter` instead of `ForwardedHeaderFiller`

Issue: SPR-17253

Issue: SPR-17233

Before this commit, Kotlin inner class nested configuration
handling thrown an IndexOutOfBoundsException due to bogus filtering
of its constructor parameter reference to an instance of the outer
class.

This commit keep constructor parameter of type INSTANCE in order to
throw a more meaningful NoSuchBeanDefinitionException.

Issue: SPR-17222

Issue: SPR-17193

Follow-up on recent commit #d537a1cf.

Issue: SPR-17243

placeholders

Spring 4.3 introduced support for registering a default embedded value
resolver for the default environment, in case of none having been
registered through post-processors (like PropertyPlaceholderConfigurer
and PropertySourcesPlaceholderConfigurer. However, the existing
documentation – stating that a static
PropertySourcesPlaceholderConfigurer bean is required in order for
values coming from @PropertySource declarations to be honored – was not
updated to reflect the change.

This commit addresses this by updating the JavaDoc for @Configuration
and @PropertySource accordingly

Issue: SPR-17212

This reverts commit fd352b84, and the
PoC will be moved to a feature branch.

1. Rename globalResources to useGlobalResources.
2. Use of global resources is mutually exlusive with explicit config.
3. Allow Consumer<HttpResources> to configure global resources.
4. Allow ConnectionProvider + LoopResources Supplier to customize
   creation and initialization.
5. Do not manage externally provided ConnectionProvider + LoopResources
   instances.

Issue: SPR-17243

Issue: SPR-17228

This commit changes the type of parameters so that HeaderAssertions
can assert expires and lastModified properly.

Issue: SPR-17194

Issue: SPR-17214

Issue: SPR-17247

Issue: SPR-17244

This commit adds decoder/message-reader tests for errors in
the source data buffer publisher. Because the tests extend
AbstractDataBufferAllocatingTestCase, they also check whether
the buffers that precede the error in the stream are properly
released.

Issue: SPR-17025

This commit fixes an issue where DataBufferUtils.join() would not
release databuffers that preceded an error signal.

Issue: SPR-17025

This commit optimizes Flux <-> Mono conversions in our codebase by
avoiding to hide that conversion from Reactor.

This tries to keep conversions sequentially so that they can be detected
by Reactor and optimized. In Spring WebFlux, this means keeping the
conversions at the edges of a method implementation (right when getting
an input parameter, and before returning it as a result). If those
conversions are made between other operators, Reactor might not be able
to detect those conversions and optimize them.

Issue: SPR-17203

This commit introduces a dependency on the Awaitility assertion
framework and makes use of asynchronous assertions in order to make
tests for asynchronous events more robust.

Issue: SPR-17211

Issue: SPR-17240