Handle clickable [url] tags in print_rich() editor output log

Since this uses `OS.shell_open()`, this allows the use of any standard URL
including `file://` paths, `mailto:`, custom protocols set up by the user, etc.

editor/editor_log.h

@@ -157,6 +157,7 @@ private:
 	Thread::ID current;
 
 	//void _dragged(const Point2& p_ofs);
+	void _meta_clicked(const String &p_meta);
 	void _clear_request();
 	void _copy_request();
 	static void _undo_redo_cbk(void *p_self, const String &p_name);