Newtypes are cumbersome in C++, so this is mostly documentation for now.
Also replace lots of questionable uses of size_t with int or types with
explicit width and add a few comments for constants.
The old stone_slab block from pre-1.14 has been renamed to
smooth_stone_slab, and the name stone_slab was reused for a new block.
Resolve the palette entry depending on the chunk's dataVersion.