This PR adds the ability to load additional images into `ex.Material`s!
  ```typescript
  const noise = new ex.ImageSource('./noise.avif');
  loader.addResource(noise);

  var waterMaterial = game.graphicsContext.createMaterial({
    name: 'water',
    fragmentSource: waterFrag,
    color: ex.Color.fromRGB(55, 0, 200, .6),
    images: {
      u_noise: noise
    }
  });
  ```