…tiled images.

ImageCache is now represented as an enum with three types:
- Err, as before.

- UntiledAuto, the fast path for untiled images using ImageRendering::Auto,
which contains a CachedImageInfo.

- Multi, the slower path used for tiled images or images that use other
ImageRendering types, which stores a hash map containing CachedImageInfo
objects for all of the variants/subsections of the image.