Support set void function to the event listener

[junwchina]

Hi, could we make a little change to ReactUnityEventParameter to support void function? sometimes, we might not want to return anything from listener.

use cases:

// Unity is started, we may do something on typescript side. 
// no return needed
const onStarted = () => {
    // do something here
}

addEventListener("OnStarted", onStarted);

The following changes is need to support this usecase:

// file: source/types/react-unity-event-parameters.ts
type ReactUnityEventParameter = string | number | undefined | void;

[jeffreylanters]

Hi! Sorry for me late response, I've been away for a couple of days. Thanks for your suggestion, I've added support for void functions in the latest release 9.4.3!