static boolean hasAnnotationMirror(Element element, String annotationName) {
    return getAnnotationMirror(element, annotationName).isPresent();
  }
Returns the {@code @AutoValue} or {@code @AutoOneOf} type parameters, with a ? for every type.
If we have {@code @AutoValue abstract class Foo<T extends Something>} then this method will
return just {@code <?>}.
value/src/main/java/com/google/auto/value/processor/AutoValueishProcessor.java