Upgrade from Smarty 3 to Smarty 4 to be PHP 8.1 compatible

Remove all Smarty4 dedicated tests, all are done in the same test file
like before

www/lib/smarty-4.1.0/libs/plugins/modifiercompiler.default.php

@@ -0,0 +1,32 @@
+<?php
+/**
+ * Smarty plugin
+ *
+ * @package    Smarty
+ * @subpackage PluginsModifierCompiler
+ */
+/**
+ * Smarty default modifier plugin
+ * Type:     modifier
+ * Name:     default
+ * Purpose:  designate default value for empty variables
+ *
+ * @link   https://www.smarty.net/manual/en/language.modifier.default.php default (Smarty online manual)
+ * @author Uwe Tews
+ *
+ * @param array $params parameters
+ *
+ * @return string with compiled code
+ */
+function smarty_modifiercompiler_default($params)
+{
+    $output = $params[ 0 ];
+    if (!isset($params[ 1 ])) {
+        $params[ 1 ] = "''";
+    }
+    array_shift($params);
+    foreach ($params as $param) {
+        $output = '(($tmp = ' . $output . ' ?? null)===null||$tmp===\'\' ? ' . $param . ' ?? null : $tmp)';
+    }
+    return $output;
+}