getKeysForElement(element) {
    return {
      id: element.getAttribute(L10NID_ATTR_NAME),
      args: JSON.parse(element.getAttribute(L10NARGS_ATTR_NAME) || null),
    };
  }
Get the `data-l10n-*` attributes from DOM elements as a two-element
array.

@param {Element} element
@returns {Object}
@private