Reorganize imports to ensure consistent ordering. This commit also
expands any `.*` static imports in favor of using fully-qualified
method references.

Issue: SPR-16968

Update all lambdas that take a single argument so that parenthesis
are never used.

Issue: SPR-16968

Update code that has accidentally used spaces instead of tabs.
Also remove all trailing whitespace.

Issue: SPR-16968

Fix a few places where `==` was accidentally used to compare
strings.

Issue: SPR-16968

Ensure that only one statement is used per line.

Issue: SPR-16968

Update `ConversionUtils` to remove conditional logic that isn't
necessary.

Issue: SPR-16968

Update classes that override `equals()` to ensure that they also
implement `hashCode()`.

Issue: SPR-16968

Ensure that `this.` is never used when accessing loggers.

Issue: SPR-16968

Ensure that `this.` is used consistently when accessing class
fields.

Issue: SPR-16968

Update all classes so that inner classes are always last. Also
ensure that utility classes are always final and have a private
constructor and make exceptions final whenever possible.

Issue: SPR-16968

Update existing catch blocks to ensure that `ex` is always used
in preference to `e` or `t` as the variable name.

Issue: SPR-16968

Update all code to use a consistent block style.

Issue: SPR-16968

Update all annotations so that each is on its own line and
consistently use the short form (i.e. don't use `value=`) when
possible.

Issue: SPR-16968

Add copyright header to `package-info.java` files and fix a few
malformed headers on existing java files.

Issue: SPR-16968

Update all files to ensure that they always end with a new line.

Issue: SPR-16968

Fix checkstyle violations for javadoc.

Issue: SPR-16968

Add checkstyle to the build to enforce Spring Framework coding
conventions. Rule suppressions are used for several classes where
relaxing the rules makes more sense than fixing them.

Issue: SPR-16968

This reverts commit c14f83e7.

Refine project specific eclipse settings and update the
instructions with details of how they can be applied.

Issues: SPR-16957

Issue: SPR-16898

Issue: SPR-16974

Issue: SPR-16972

This commit upgrades the gradle-wrapper.jar.

Issue: SPR-16475

Issue: SPR-16898

Includes Kotlin 1.2.50, RxJava 2.1.15 and Protobuf 3.6.

Issue: SPR-16475

Issue: SPR-16898

In SPR-16892, the `EncoderHttpMessageWriter` has been improved to write
`"Content-Length"` HTTP response headers if the response body is of type
`Mono` (i.e. the actual content length is easily accessible without
buffering a possibly large response body). That change was relying on
the fact that the server side is using a `ChannelSendOperator` to delay
the writing of the body until the first signal is received.

This strategy is not effective on the client side, since no such channel
operator is used for `WebClient`. This commit improves
`EncoderHttpMessageWriter` and delays, for `Mono` HTTP message bodies
only, the writing of the body so that we can write the
`"Content-Length"` header information once we've got the body resolved.

Issue: SPR-16949

* pr/1860:
  Fix broken link to CONTRIBUTING.md

Closes gh-1860

Issue: SPR-16898

Issue: SPR-16947

The wording changed from "Can not find" to "Cannot find" via PR #1682

Issues: SPR-16947

Issue: SPR-12458

Issue: SPR-12458