this significantly reduces the size of schemas when state remaps are used (see pmmp/BedrockBlockUpgradeSchema@85b83b360e).
in addition, this will likely offer a substantial performance and memory saving when walls get flattened, which will eventually happen.
this reduces the footprint of RuntimeBlockMapping by a further 1 MB, as well as simplifying various parts of the code, and solidifying the immutability guarantee of BlockStateData.
