Deprecate Twig Bundle base_template_class option

Author: Steveb-p

src/Symfony/Bundle/TwigBundle/DependencyInjection/Configuration.php

@@ -129,7 +129,11 @@ private function addTwigOptions(ArrayNodeDefinition $rootNode): void
             ->children()
                 ->scalarNode('autoescape_service')->defaultNull()->end()
                 ->scalarNode('autoescape_service_method')->defaultNull()->end()
-                ->scalarNode('base_template_class')->example('Twig\Template')->cannotBeEmpty()->end()
+                ->scalarNode('base_template_class')
+                    ->setDeprecated('symfony/twig-bundle', '7.1')
+                    ->example('Twig\Template')
+                    ->cannotBeEmpty()
+                ->end()
                 ->scalarNode('cache')->defaultValue('%kernel.cache_dir%/twig')->end()
                 ->scalarNode('charset')->defaultValue('%kernel.charset%')->end()
                 ->booleanNode('debug')->defaultValue('%kernel.debug%')->end()