function escapeIcuMessage(message) {
  return message
    .replace(/'/g, `''`)
    .replace(/\\{/g, `'{`)
    .replace(/\\}/g, `'}`);
}
Our strings were made when \ was the escape character, but now it is '. To avoid churn,
let's convert to the new style in memory.
@param {string} message
@return {string}