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.cat.php

@@ -0,0 +1,28 @@
+<?php
+/**
+ * Smarty plugin
+ *
+ * @package    Smarty
+ * @subpackage PluginsModifierCompiler
+ */
+/**
+ * Smarty cat modifier plugin
+ * Type:     modifier
+ * Name:     cat
+ * Date:     Feb 24, 2003
+ * Purpose:  catenate a value to a variable
+ * Input:    string to catenate
+ * Example:  {$var|cat:"foo"}
+ *
+ * @link   https://www.smarty.net/manual/en/language.modifier.cat.php cat
+ *           (Smarty online manual)
+ * @author Uwe Tews
+ *
+ * @param array $params parameters
+ *
+ * @return string with compiled code
+ */
+function smarty_modifiercompiler_cat($params)
+{
+    return '(' . implode(').(', $params) . ')';
+}