See gh-16421

Closes gh-16421

See gh-16418

Closes gh-16333

See gh-16418

Closes gh-16351

Closes gh-16354

Closes gh-16353

Closes gh-16418

Remove a few items that are no longer necessary.

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

* pr/16174:
  Replace ${sys:PID} with %pid in log4j2 configuration

Replacing property sys:PID which was set in the code with the default
log4j2 Pattern in log4j2.xml and log4j2-file.xml files.

Closes gh-16174

* pr/16327:
  Polish "Add Spring-specific styling to Gradle Plugin's documentation"
  Add Spring-specific styling to Gradle Plugin's documentation

Closes gh-16327

This commit replaces the default Asciidoctor styling with
Spring specific styling.

First, we need to unzip the contents of the Spring Asciidoctor
documentation resources provided by the
`io.spring.docsresources:spring-docs-resources` distribution zip. This
is done in a `/target/refdocs` folder. We then copy all files from
`src/main/asciidoc` to the same location, and then launch the generation
process.

See gh-16327

Closes gh-16326

Closes gh-16415

Closes gh-16413

See gh-16068

* gh-16410:
  Polish "Update CORS handling according to Framework changes"
  Update CORS handling according to Framework changes

Closes gh-16410

See gh-16410

This commit updates CORS handling according to Framework changes
introduced via [1]. It also fixes tests according to the new behavior.

See gh-16410

[1] https://github.com/spring-projects/spring-framework/commit/d27b5d0ab6e8b91a77e272ad57ae83c7d81d810b.