Rewrite Stream.collect(Collectors.toUnmodifiableList()) to Stream.toList()

[Laurens-W]

What's changed?

Continuation of openrewrite/rewrite-static-analysis#167, which may be declined at this point
Adding a recipe that rewrites Java 11 Stream.collect(Collectors.toUnmodifiableList()) to Java 16 Stream.toList() with an optional toggle to include Stream.collect(Collectors.toList()) so no harm is done initially.

What's your motivation?

I asked on slack if there was an opposing recipe to replacestreamtolistwithcollect, we came to the conclusion that it does not exist but does seem justifiable to have.

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

Anyone you would like to review specifically?

@timtebeek @joanvr

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 added the license header to any new files through ./gradlew licenseFormat
• I've used the IntelliJ IDEA auto-formatter on affected files

[timtebeek]

Thanks a lot @Laurens-W , both for suggesting the recipe and implementing it. I've done a few polishing changes, but otherwise a direct success. :)