Parse inline checkstyle config from maven-checkstyle-plugin

[tobli]

What's changed?

Inline checkstyle config from maven-checkstyle-plugin can now be parsed, in addition to reading file references from the configLocation tag.

What's your motivation?

Support more of the various config options that exist for maven-checkstyle-plugin, to capture more style instructions that exist in existing codebases.

Anything in particular you'd like reviewers to focus on?

I didn't think of an obvious positive test case, but I'm happy to take suggestions. For now, just look for the absence of parsing errors.

Checklist

• I've added unit tests to cover both positive and negative cases
• I've read and applied the recipe conventions and best practices
• I've used the IntelliJ IDEA auto-formatter on affected files

[timtebeek]

Thanks for working out what's required to parse inline config; nice to be able to cover this variant as well!

[tobli]

Thanks for working out what's required to parse inline config; nice to be able to cover this variant as well!

My follow up is parsing check style files from plugin dependency jars. That requires some more refactoring, but with this the diff is smaller. I can post a rough draft PR soon for early feedback.