Update model for interfaces extending interfaces (#4663)

* Add new test

* Apply suggestions from code review

* Fix test

* Clean up

* Added javadoc

---------

Co-authored-by: Ralph-Sanders <ralph.sanders@ibm.com>
Co-authored-by: Tim te Beek <timtebeek@gmail.com>

rewrite-java/src/main/java/org/openrewrite/java/tree/J.java

@@ -1222,6 +1222,12 @@ public ClassDeclaration withPrimaryConstructor(@Nullable List<Statement> primary
         @Nullable
         JLeftPadded<TypeTree> extendings;
 
+        /**
+         * This is used to access the parent class.
+         *
+         * @return The parent class of the ClassDeclaration. If the ClassDeclaration is a class, this will return the
+         * class specified by the 'extends' keyword. If the ClassDeclaration is an interface, this will return null.
+         */
         public @Nullable TypeTree getExtends() {
             return extendings == null ? null : extendings.getElement();
         }
@@ -1233,6 +1239,13 @@ public ClassDeclaration withExtends(@Nullable TypeTree extendings) {
         @Nullable
         JContainer<TypeTree> implementings;
 
+        /**
+         * This is used to access the parent interfaces.
+         *
+         * @return A list of the parent interfaces of the ClassDeclaration. If the ClassDeclaration is a class, this
+         * will return the interfaces specified by the 'implements' keyword. If the ClassDeclaration is an interface,
+         * this will return the interfaces specified by the 'extends' keyword.
+         */
         public @Nullable List<TypeTree> getImplements() {
             return implementings == null ? null : implementings.getElements();
         }