[Feature Request] OnClickAsObservable for UI Toolkit

[ynaoto]

Thanks for the great library!
If there is an OnClickAsObservable that supports the UI Toolkit I would be very happy.

[georg-walkingtreegames]

How about using this simple extension method:

public static Observable<Button> ClickedAsObservable(this Button button)
{
    return Observable.FromEvent<Action, Button>(h => () => h(button),
        h => button.clicked += h,
        h => button.clicked -= h);
}