RemoveUnusedImports should not remove imports for used nested classes

[Laurens-W]

What's changed?

Some improvements to handling nested inner class imports

What's your motivation?

• Fixes org.openrewrite.java.RemoveUnusedImports should not removed imports for public static inner class usage #3283

Anyone you would like to review specifically?

@timtebeek

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]

Two new curious failures in ChangeTypeTest: https://ge.openrewrite.org/s/2lfbsonpxu4f6/tests/overview?outcome=FAILED
I guess you can see why I was hesitant to change rewrite-java/src/main/java/org/openrewrite/java/tree/JavaType.java ;)

[timtebeek]

Great to see these subtle fixes; should help make these recipes something we can enforce going forward.

[timtebeek]

Let's merge when you're done validating against those Spring projects, just to be safe