Add recipe to change logger fields to private

[jhl221123]

What's changed?

This PR introduces ChangeLoggersToPrivate, a new recipe enforcing private visibility for logger fields.

What's your motivation?

Addresses issue #219, promoting better encapsulation of logging mechanics.

• Fixes Loggers should be always private #219

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

Correctness of modifier changes across different logger types and existing modifiers.

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]

Thanks a lot for the help here @jhl221123 ! I've added some light polishing commits. Preconditions should help keep this recipe performant, by only traversiong through compilation units that use a logger at all. The ListUtils is a slightly more expressive way of manipulating elements. And the prefix wrangling that was there previously is no longer necessary. I've also added your recipe to be included with our SLF4J best practices, such that folks do no have to specifically seek out this recipe to get the benefits, but can run the broader best practices.

We acknowledge that if folks were to use the logger field from another class that might now break; we can optionally follow up with a change to make this a scanning recipe that detects such usage, and in those cases does not make any changes. I'd consider that rare though, and tolerable for a best practices recipe.

[jhl221123]

@timtebeek, Thanks for the polishing commits and for merging this! I've learned a lot more about OpenRewrite thanks to your guidance during this process. I'll be sure to keep these points in mind for even better contributions next time. Thank you!

[timtebeek]

Thanks a lot! Looking forward to what you'll do next. :D