[MSHARED-1033] Add resources required for automatic formatting and import sorting

[gnodet]

Proposal to incorporate the eclipse xml formatter config into maven-shared-resources so that we can use it with auto-formatting plugins (see apache/maven-resolver#147 and apache/maven#824).
This file would become the reference and the site should be updated to reflect that with apache/maven-site#329).

[slawekjaranowski]

There is also references to IDE formaters on site:
https://maven.apache.org/developers/conventions/code.html

Do we need some synchronization for its?

File is diferent:
https://maven.apache.org/developers/maven-eclipse-codestyle.xml

[gnodet]

IIRC, I've had to modify some rules in order to comply with checkstyle, but I'll do a diff and get back.

[gnodet]

There is also references to IDE formaters on site: https://maven.apache.org/developers/conventions/code.html

Do we need some synchronization for its?

File is diferent: https://maven.apache.org/developers/maven-eclipse-codestyle.xml

@slawekjaranowski

Yes, I would suggest that the web page should point to the GitHub file once it has been included, but I can raise a different PR for the website later.

As for the differences, those are really changes to make sure the automatic formatting complies with the checkstyle rules that are defined in the maven_checks.xml file. This fixes alignment for various use cases to 16 (so not unsplit lines, alignment on the left...) so that long lines can be automatically reformatted. I did try with the settings on the web site, but some lines can not be automatically formatted and comply with the checkstyle rules. There are also missing settings from recent JDK (lambda...)

[gnodet]

I've reworked this small commit to include the 3 files from maven-site, with an additional plain header file that should be useful.