Using PHP functions as modifiers now triggers a deprecation notice (#814)

Fixes #813

libs/plugins/modifiercompiler.round.php

@@ -0,0 +1,23 @@
+<?php
+
+/**
+ * Smarty plugin
+ *
+ * @package    Smarty
+ * @subpackage PluginsModifierCompiler
+ */
+/**
+ * Smarty round modifier plugin
+ * Type:     modifier
+ * Name:     round
+ * Purpose:  Returns the rounded value of num to specified precision (number of digits after the decimal point)
+ *
+ * @link   https://www.smarty.net/docs/en/language.modifier.round.tpl round (Smarty online manual)
+  *
+ * @param array $params parameters
+ *
+ * @return string with compiled code
+ */
+function smarty_modifiercompiler_round($params) {
+    return 'round((float) ' . $params[0] . ', (int) ' . ($params[1] ?? 0) . ', (int) ' . ($params[2] ?? PHP_ROUND_HALF_UP) . ')';
+}