static arrayStringify_(arr) {
    const terms = [];
    for (let index = 0; index < arr.length; index++) {
      const escapedKey = index.toString();
      const value = arr[index];
      if (value !== undefined) {
        const escapedValue =
            shaka.util.ObjectUtils.alphabeticalKeyOrderStringify(value);
        if (escapedValue) {
          terms.push(escapedKey + ':' + escapedValue);
        }
      }
    }
    return '[' + terms.join(',') + ']';
  }
Helper for alphabeticalKeyOrderStringify for arrays.

This could itself be JSON.stringify, except we want objects within the
array to go through our own stringifiers.

@param {!Array} arr
@return {string}
@private