Issue: SPR-16324

Issue: SPR-16322

Issue: SPR-16266

Issue: SPR-16356

Issue: SPR-16315

Issue: SPR-16353

Issue: SPR-16352

Issue: SPR-13481

Issue SPR-16248

Issue: SPR-16255

Issue: SPR-16347

Issue: SPR-16343

Issue: SPR-16250

Issue: SPR-16278

Issue: SPR-16284

Issue: SPR-16281

Issue: SPR-16334

Issue: SPR-16298

The issue was introduced very recently with commit #7035ee but never
released.

Issue: SPR-16350

Issue: SPR-16260

Cross-reference sections on HttpMessageReader/Writer and
HttpMessageConverter and improve the content.

Issue: SPR-16260

Issue: SPR-16339

Issue: SPR-13574

Issue: SPR-16328

Since type erasure can be fixed only when using
ParameterizedTypeReference based Java methods, RestOperations and
WebFlux API documentation should be updated to specify which extensions
are subject to type erasure, and which are not.

Issue: SPR-16273

* pr/1627:
  Polish Javadoc

Closes gh-1627

This allows us to confirm 0.7.3 fixes and run tests against the latest
ahead of an upgrade to Reactor Netty 0.8 snapshots.

The fix for #231 and #240 are confirmed but unfortunately test case for

This commit moves the ResolvableType field from HttpEntity to
PublisherEntity, a new entity type defined in MultipartBodyBuilder.
With this change, the scope of the ResolvableType is limited to
multipart-related code, instead of becoming part of the complete
HttpEntity hierarchy.

Issue: SPR-16307

This commit adds new header assertions for `WebTestClient`.

`doesNotExist` tests that a given header is not present:

    .expectHeader().doesNotExist("Cache-Control");

`contentTypeCompatibleWith` tests for MediaType compatibility:

    .expectHeader().contentTypeCompatibleWith("text/*");

Issue: SPR-16285

This commit uses the changes in the previous commit to support
Publishers as parts for multipart data.

Issue: SPR-16307

This commit adds a ResolvableType field to HttpEntity, in order to
support Publishers as multipart data. Without the type, the
MultipartHttpMessageWriter does not know which delegate writer to use to
write the part.

Issue: SPR-16307