static ImmutableList<ExecutableElement> toPrettyStringMethods(
      TypeElement element, Types types, Elements elements) {
    return getLocalAndInheritedMethods(element, types, elements).stream()
        .filter(method -> toPrettyStringAnnotation(method).isPresent())
        .collect(toImmutableList());
  }
Returns the {@link com.google.auto.value.extension.toprettystring.ToPrettyString} annotated
method for a type.
value/src/main/java/com/google/auto/value/extension/toprettystring/processor/ToPrettyStringMethods.java