getExportSpecifiersByDir = async dirPath => {
  const fileNames = await getSortedJsFileNamesInDir(path.join(dirPath, '*.js'));
  // @ts-ignore
  const exports = await asyncConcurrentForEach(fileNames, async fileName => {
    const filePath = path.resolve(dirPath, fileName);
    return getExportSpecifiersByFile(filePath);
  });
  return exports.flat().sort(byStringAscendingSort);
}
Get export specifiers for all the js files in a directory given with `dirPath`
@param {string} dirPath Directory path
@returns {Promise<string[]>}