Update Twig from 1.35.0 to 1.42.4 (PHP 5.5 is now required!)

This fixes some errors on PHP 7.4 and contains even more fixes
Also bumped PHP version to 5.5 as Twig requires it.

system/libs/Twig/NodeVisitor/NodeVisitorInterface.php

@@ -0,0 +1,50 @@
+<?php
+
+/*
+ * This file is part of Twig.
+ *
+ * (c) Fabien Potencier
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Twig\NodeVisitor;
+
+use Twig\Environment;
+
+/**
+ * Interface for node visitor classes.
+ *
+ * @author Fabien Potencier <fabien@symfony.com>
+ */
+interface NodeVisitorInterface
+{
+    /**
+     * Called before child nodes are visited.
+     *
+     * @return \Twig_NodeInterface The modified node
+     */
+    public function enterNode(\Twig_NodeInterface $node, Environment $env);
+
+    /**
+     * Called after child nodes are visited.
+     *
+     * @return \Twig_NodeInterface|false|null The modified node or null if the node must be removed
+     */
+    public function leaveNode(\Twig_NodeInterface $node, Environment $env);
+
+    /**
+     * Returns the priority for this visitor.
+     *
+     * Priority should be between -10 and 10 (0 is the default).
+     *
+     * @return int The priority level
+     */
+    public function getPriority();
+}
+
+class_alias('Twig\NodeVisitor\NodeVisitorInterface', 'Twig_NodeVisitorInterface');
+
+// Ensure that the aliased name is loaded to keep BC for classes implementing the typehint with the old aliased name.
+class_exists('Twig\Environment');