Avoid repeated work in NodeGrantDatabaseStorage::alterQuery

The NodeGrantDatabaseStorage::alterQuery() method appears to be doing extra work which could be avoided: it builds a constant array of grants in a loop on all tables in a query instead of building it just once:

    $grants = node_access_grants($op, $account);
    foreach ($tables as $nalias => $tableinfo) {
      $table = $tableinfo['table'];
      if (!($table instanceof SelectInterface) && $table == $base_table) {
        // Set the subquery.
        $subquery = $this->database->select('node_access', 'na')
          ->fields('na', ['nid']);

        // If any grant exists for the specified user, then user has access to the
        // node for the specified operation.
        $grant_conditions = static::buildGrantsQueryCondition($grants);

Some CPU use could be avoided by factoring the buildGrandsQueryCondition out of the loop, as that is a pure function which takes invariant arguments.

Similarly references and calls to \Drupal::languageManager()->isMultilingual()) are invariant and could be taken out of the loop.