Check for is granted impersonator on Symfony >= 5.4 (#1627)

Author: jordisala1991

src/Resources/views/Admin/Core/user_block.html.twig

@@ -15,7 +15,11 @@ file that was distributed with this source code.
         {% set _logout_uri = url('sonata_user_admin_security_logout') %}
         {% set _logout_text = 'user_block_logout'|trans({}, 'SonataUserBundle') %}
 
-        {% if is_granted('ROLE_PREVIOUS_ADMIN') and sonata_user.isImpersonatingEnabled %}
+        {# TODO: Remove the check for the IS_IMPERSONATOR constant when dropping support for Symfony 4.4 #}
+        {% if sonata_user.isImpersonatingEnabled and (constant('Symfony\\Component\\Security\\Core\\Authorization\\Voter\\AuthenticatedVoter::IS_IMPERSONATOR') is defined ?
+            is_granted('IS_IMPERSONATOR') :
+            is_granted('ROLE_PREVIOUS_ADMIN'))
+        %}
             {% set _bg_class = 'bg-light-green' %}
             {% set _logout_uri = url(sonata_user.impersonatingRoute, sonata_user.impersonatingRouteParameters|merge({'_switch_user': '_exit'})) %}
             {% set _logout_text = 'switch_user_exit'|trans({}, 'SonataUserBundle') %}