Migrate to Spotless from Checkstyle

[SirEndii]

Advanced Peripherals currently uses the gradle checkstyle plugin to be able to maintain a uniform code style in the project.

But there are two main reasons why I want to switch from checkstyle to spotless.

• Spotless has way more features
  Spotless has a wider range of features. One among them is the spotlessApply task to just fix the style issues automatically while maintaining license headers.
• Advanced custom steps
  If I need custom steps, I can create custom steps using FormatterStep and FormatterFunc using spotless, which also works for the spotlessApply task. Checkstyle "only" allows custom regex checks. Which isn't bad, but I just can do more with these java based custom steps.

Currently, there aren't any custom steps. The eclipse formatter used provides a decent code style I really like. But I will consider adding custom steps for our annotation and one-liner if statement guidelines

[SirEndii]

Currently waiting for any feedback on diffplug/spotless#2095

I am unable to use https://github.com/diffplug/spotless/blob/main/plugin-gradle/README.md#retroactively-slurp-years-from-git-history