VRAM + Display Mode abstractions?

[Lokathor]

It's quite difficult to make any useful abstractions over VRAM for all possible video modes, but I think that we can at least do a good effort if we focus on just one mode at a time.

My first thought is that we can make a sub-module for each display mode and then fill it with display helpers and constants relevant to that mode.

Are there other good options? I also had the idea to try and make TiledGraphics and BitmapGraphics traits that we implement onto empty structs that represent each display mode, but I think even among Tiled and Bitmap modes there's not quite enough similarity to make that very useful.