[ticket/11997] Use path_helper in in foo/bar extension for redirect URLs

By using path_helper's clean_url() method, we'll be able to properly check
the full URL instead of just parts of the expected URL.

PHPBB3-11997

tests/functional/fixtures/ext/foo/bar/config/services.yml

@@ -3,6 +3,7 @@ services:
         class: foo\bar\controller\controller
         arguments:
             - @controller.helper
+            - @path_helper
             - @template
             - %core.root_path%
             - %core.php_ext%