Includes: Added back support for parse theme event

Managed to do this in an API-compatible way although resuling output may
differ due to new dom handling in general, although user content is used
inline to remain as comptable as possible.

app/Theming/ThemeService.php

@@ -48,6 +48,14 @@ class ThemeService
         return null;
     }
 
+    /**
+     * Check if there are listeners registered for the given event name.
+     */
+    public function hasListeners(string $event): bool
+    {
+        return count($this->listeners[$event] ?? []) > 0;
+    }
+
     /**
      * Register a new custom artisan command to be available.
      */