feat: Add macOS screenshot support

[MaxLeiter]

Usage:

  const screenshotBuffer = OverlayController.screenshot();
    const screenshotImage = nativeImage.createFromBuffer(screenshotBuffer, {
      width: OverlayController.targetBounds.width,
      height: OverlayController.targetBounds.height,
    });

Here is a result from the demo app:

Colors are a bit off but I'm not sure why; you can see it in the traffic light buttons. I might need to adjust the CGColorSpaceRef