Fix handling OBS_FRONTEND_EVENT_TRANSITION_CHANGED

When handling frontend events, DispatchJSEvent expects JSON passed as a
std::string. An unquoted string is not valid JSON. To get valid JSON, we
can build a JSON object like in OBS_FRONTEND_EVENT_SCENE_CHANGED and
pass the result of dump() to DispatchJSEvent.

obs-browser-plugin.cpp

@@ -642,7 +642,9 @@ static void handle_obs_frontend_event(enum obs_frontend_event event, void *)
 		if (!name)
 			break;
 
-		DispatchJSEvent("obsTransitionChanged", name);
+		nlohmann::json json = {{"name", name}};
+
+		DispatchJSEvent("obsTransitionChanged", json.dump());
 		break;
 	}
 	case OBS_FRONTEND_EVENT_TRANSITION_LIST_CHANGED: {