src/language-js/utils.js/isFlowAnnotationComment
function isFlowAnnotationComment(text, typeAnnotation, options) {
  const start = options.locStart(typeAnnotation);
  const end = skipWhitespace(text, options.locEnd(typeAnnotation));
  return (
    text.slice(start, start + 2) === "/*" && text.slice(end, end + 2) === "*/"
  );
}