setFlags(flags) {
    this.flags = Number.isInteger(flags) && flags > 0 ? flags : 0;
    if (
      this.flags & AnnotationFlag.INVISIBLE &&
      this.constructor.name !== "Annotation"
    ) {
      // From the pdf spec v1.7, section 12.5.3 (Annotation Flags):
      //   If set, do not display the annotation if it does not belong to one of
      //   the standard annotation types and no annotation handler is available.
      //
      // So we can remove the flag in case we have a known annotation type.
      this.flags ^= AnnotationFlag.INVISIBLE;
    }
  }
Set the flags.

@public
@memberof Annotation
@param {number} flags - Unsigned 32-bit integer specifying annotation
                        characteristics
@see {@link shared/util.js}