This makes it possible to change the resolution of the LOS system, relative to the word size. It is currently 4 (== terrain tile).
- LosTile has been renamed LosRegion (mostly because it was needlessly confusing, it's not a "tile" in the same sense as a "terrain tile". Those store entity counts and dirtiness.
- LosState is now said to be using "los vertices". This is because we do have a resolution, and unit's position are rounded to the nearest vertex when computing visibility, which is more similar to a vertex than a tile behaviour.
- All usage of TERRAIN_TILE_SIZE is updated to LOS_TILE_SIZE.
This supports both lower and higher resolutions (up to 1 tile per meter). I don't think we need to change the current value, though we could actually consider bumping it up to 8 IMO.
Here's what the game looks like with a 1-1 resolution:
Part of #5566.