8309821: Link to hidden classes section in Class specification for Class::isHidden

Reviewed-by: iris, rriggs

src/java.base/share/classes/java/lang/Class.java

@@ -4720,6 +4720,7 @@ public final class Class<T> implements java.io.Serializable,
      *
      * @since 15
      * @see MethodHandles.Lookup#defineHiddenClass
+     * @see Class##hiddenClasses Hidden Classes
      */
     @IntrinsicCandidate
     public native boolean isHidden();