Migrate to Kotlin 2.1

[barbulescu]

What's changed?

What's your motivation?

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

Anyone you would like to review specifically?

Have you considered any alternatives or workarounds?

Any additional context

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]

Adding a quick note here that we've since moved this repository into openrewrite/rewrite; let us know if you'd like help porting over the work you have done here!