Besides adding a number of experimental block types for the 1.21 preview,
Minecraft 1.20.3 also renamed the "grass" block to "short grass"
internally. Add the new block name to avoid warnings during generation.
Get rid of the arbitrary bin/lib split and instead move as much as
possible into the bin crate, which becomes the main crate again.
The types and NBT handling are moved into separate crates, so they can
be reused by nbtdump and regiondump.