Recipe to move classes to their own files

What problem are you trying to solve?

Code readability.

Describe the situation before applying the recipe

Book.java

public class Book {
   public String title;
   public Author author;
}

class Author {
    public String firstName;
    public String lastName;
}

Describe the situation after applying the recipe

Book.java

public class Book {
   public String title;
   public Author author;
}

Author.java

class Author {
    public String firstName;
    public String lastName;
}

Context

Interfaces should be included too.

Use the Book.java and Author.java examples as the behavioral starting point, then locate the recipe entry point and comparable OpenRewrite recipes in the repository. Verify the recipe separates nested or additional classes into their own files and handles interfaces too; finish by running the relevant existing recipe tests or adding coverage if none is identified.