function gatherIcuPlaceholderNames(icuTemplate) {
  const resultSet = new Set();
  let match = null;

  while (match = ICU_PLACEHOLDER_GLOBAL_RE.exec(icuTemplate)) {
    resultSet.add(match[1]);
  }
  return resultSet;
}
@param {string} icuTemplate
@return {!Set<string>} contains placeholder names found in icuTemplate