Update the eclipse setup files and contributing instructions for
compatibility with the latest Eclipse 2019-03 release. This commit
reverts the use the HTTPS in the `.setup` file namespace (since it
breaks the setup editor). The `xsi:schemaLocation` section still
uses HTTPS for actual XSD resolution.
See gh-16245
Use `spring-javaformat` to format and check code. Code formatting can
now be applied using the `spring-javaformat-maven-plugin` from the
command line. Existing checkstyle rules have also been replaced and
the CONTRIBUTING.adoc file has been updated.
Closes gh-13255
dreis2211
Phillip Webb
Andy Wilkinson