Source Code Tidy Up - How to proceed?

[Oliver-Loeffler]

As we now have Checkstyle in place, we have a powerful tool to detect and avoid tiresome formatting mistakes.
When running Checkstyle one will receive lots of warnings.

What would be a good way to get rid of those?

• Many small PRs dedicated to clean up formatting?
• Apply path finder rule in feature PRs and clean up there?
• Run one big PR with having all Checkstyle warnings eliminated in one run?

The 3rd approach would have the advantage, that contributors & maintainers can use Checkstyle as a serious tool.
The second approch would bloat the feature PRs with formalities and distract from actual work. The first one would work and just prolong the bad situation.

Are there any other ideas or proposals on how to proceed towards a cleaner codebase?
My goal here is to avoid this formatting stuff in PRs and codereviews. What do you think?
I personally favor approach 3, one big action.