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/Node/Expression/NullCoalesceExpression.php

@@ -0,0 +1,62 @@
+<?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\Node\Expression;
+
+use Twig\Compiler;
+use Twig\Node\Expression\Binary\AndBinary;
+use Twig\Node\Expression\Test\DefinedTest;
+use Twig\Node\Expression\Test\NullTest;
+use Twig\Node\Expression\Unary\NotUnary;
+use Twig\Node\Node;
+
+class NullCoalesceExpression extends ConditionalExpression
+{
+    public function __construct(\Twig_NodeInterface $left, \Twig_NodeInterface $right, $lineno)
+    {
+        $test = new DefinedTest(clone $left, 'defined', new Node(), $left->getTemplateLine());
+        // for "block()", we don't need the null test as the return value is always a string
+        if (!$left instanceof BlockReferenceExpression) {
+            $test = new AndBinary(
+                $test,
+                new NotUnary(new NullTest($left, 'null', new Node(), $left->getTemplateLine()), $left->getTemplateLine()),
+                $left->getTemplateLine()
+            );
+        }
+
+        parent::__construct($test, $left, $right, $lineno);
+    }
+
+    public function compile(Compiler $compiler)
+    {
+        /*
+         * This optimizes only one case. PHP 7 also supports more complex expressions
+         * that can return null. So, for instance, if log is defined, log("foo") ?? "..." works,
+         * but log($a["foo"]) ?? "..." does not if $a["foo"] is not defined. More advanced
+         * cases might be implemented as an optimizer node visitor, but has not been done
+         * as benefits are probably not worth the added complexity.
+         */
+        if (\PHP_VERSION_ID >= 70000 && $this->getNode('expr2') instanceof NameExpression) {
+            $this->getNode('expr2')->setAttribute('always_defined', true);
+            $compiler
+                ->raw('((')
+                ->subcompile($this->getNode('expr2'))
+                ->raw(') ?? (')
+                ->subcompile($this->getNode('expr3'))
+                ->raw('))')
+            ;
+        } else {
+            parent::compile($compiler);
+        }
+    }
+}
+
+class_alias('Twig\Node\Expression\NullCoalesceExpression', 'Twig_Node_Expression_NullCoalesce');