Rendre compatible ce bundle avec Symfony 5.4

[klnjmm]

Deux changements apportés pour que ce bundle fonctionne avec Symfony 5.4 :

• la déclaration de la configuration

A tree builder without a root node is deprecated since Symfony 4.2 and will not be supported anymore in 5.0

• La modification de méthodes liées à la version 3 de Twig

Using the "Twig_Extension" class is deprecated since Twig version 2.7, use "Twig\Extension\AbstractExtension" instead.

As of Twig 2.x, the Twig_SimpleFunction class is deprecated and will be removed in Twig 3.x (use \Twig\TwigFunction instead). In Twig 2.x, Twig_SimpleFunction is just an alias for \Twig\TwigFunction.