docs: private static Set<TypeMirror> topLevelTypes(Types typeUtil, Set<TypeMirror> types) {
      return types
          .stream()
          .map(typeMirror -> MoreElements.asType(typeUtil.asElement(typeMirror)))
          .map(typeElement -> topLevelType(typeElement).asType())
          .collect(toCollection(TypeMirrorSet::new));
    }