static fromMillis(count, opts) {
    return Duration.fromObject({ milliseconds: count }, opts);
  }
Create Duration from a number of milliseconds.
@param {number} count of milliseconds
@param {Object} opts - options for parsing
@param {string} [opts.locale='en-US'] - the locale to use
@param {string} opts.numberingSystem - the numbering system to use
@param {string} [opts.conversionAccuracy='casual'] - the conversion system to use
@return {Duration}