Fix frontend save template options error (joomla#45199)

Thanks for the fix @joomdonation and @exlemor & @krishnaGandhi11 for tests

Author: joomdonation

administrator/components/com_templates/src/Controller/StyleController.php

@@ -58,9 +58,9 @@ public function save($key = null, $urlVar = null)
             $item = $model->getItem($this->app->getTemplate(true)->id);
 
             // Setting received params
-            $item->set('params', $data);
+            $item->params = $data;
 
-            $data = $item->getProperties();
+            $data = get_object_vars($item);
             unset($data['xml']);
 
             $key = $table->getKeyName();