Support record classes in annotation processor

[xeals]

Record classes are unmodifiable data class introduced in Java 16 and included in the recent LTS version Java 17. Since records are a new syntax for Java, they generate an ElementKind.RECORD AST element instead of ElementKind.CLASS and are not supported by the current visitor.

Javadoc for a record is the same as a regular class, except it may include @param fields referring to record components:

/**
 * Example class.
 *
 * @param a first component input
 * @param b second input
 */
public class Foo(boolean a, String b) {

  /** Alternate constructor */
  public Foo(boolean a) {
    this(a, null);
  }
}

General thoughts:

• As best as I can tell, the compiler doesn't attach any docs to the generated fields or methods, or to the primary constructor
• There's no way to directly comment the record components

Depending on how an implementation might balance representation vs. intent:

• The class docs could be re-applied to the primary constructor, which can be determined by the GENERATED or RECORD flags set on the method (which I think is specified, but I can't find the exact mention in the JVM spec)
• @param tags from the primary constructor could be applied to the fields and/or methods

[dnault]

The 0.13.0 release will add basic support for records. Record class docs will be retained, as well as docs for secondary constructors and other methods and fields defined in the record.

There will also be a new method ClassJavadoc.getRecordComponents() that returns any @param tags from the class docs.

I filed #60 for attaching docs to the canonical constructor and generated component accessors.

[dnault]

Version 0.13.0 with basic support for records is now live on Maven Central.