Issue #3306686 by e0ipso: Make URL generator serializable

namespace Drupal\cl_server;

use Drupal\Core\DependencyInjection\DependencySerializationTrait;

use Drupal\Core\File\FileUrlGeneratorInterface;

use Drupal\Core\Http\RequestStack;

use Drupal\Core\Url;

class FileUrlGenerator implements FileUrlGeneratorInterface {

  use DependencySerializationTrait;

  /**

   * The file generator.

   *