migration symfony 5 4 (#300)

* symfony 5.4 (diff dev)

* symfony 5.4 (working)

* symfony 5.4 (update autoload)

* symfony 5.4 (remove swiftmailer mailer implementation)

* symfony 5.4 (php doc and split Global accessor class)


### Impacted packages:

composer require php:">=7.2.5 <8.0.0" symfony/console:5.4.* symfony/dotenv:5.4.* symfony/framework-bundle:5.4.* symfony/twig-bundle:5.4.* symfony/yaml:5.4.* --update-with-dependencies

composer require symfony/stopwatch:5.4.* symfony/web-profiler-bundle:5.4.* --dev --update-with-dependencies

lib/symfony/var-dumper/Caster/ProxyManagerCaster.php

@@ -0,0 +1,33 @@
+<?php
+
+/*
+ * This file is part of the Symfony package.
+ *
+ * (c) Fabien Potencier <fabien@symfony.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Symfony\Component\VarDumper\Caster;
+
+use ProxyManager\Proxy\ProxyInterface;
+use Symfony\Component\VarDumper\Cloner\Stub;
+
+/**
+ * @author Nicolas Grekas <p@tchwork.com>
+ *
+ * @final
+ */
+class ProxyManagerCaster
+{
+    public static function castProxy(ProxyInterface $c, array $a, Stub $stub, bool $isNested)
+    {
+        if ($parent = get_parent_class($c)) {
+            $stub->class .= ' - '.$parent;
+        }
+        $stub->class .= '@proxy';
+
+        return $a;
+    }
+}