[mac] Mouse Up/Down events triggering on move

[thomasuster]

1. Add the following to a nme/sample project.

stage.addEventListener(MouseEvent.MOUSE_UP, onMouseUp);
stage.addEventListener(MouseEvent.MOUSE_DOWN, onMouseDown);
...
    function onMouseUp(event:MouseEvent):Void {
        trace("mouse up");
    }

    function onMouseDown(event:MouseEvent):Void {
        trace("mouse down");
    }

2. haxelib run nme mac
3. Move mouse around without clicking
   Expected: Nothing should print
   Result: Both seem to trigger when the mouse starts and stops

[thomasuster]

FYI on MacOS Catalina 10.15.5