Allow injecting ID mapping tables into SubChunkConverter

[dktapps]

In a sane world where block conversion is handled properly, we're almost never going to want the original block IDs that were contained in an anvil, mcregion or legacy leveldb chunk, so the palette will need to be converted in such cases. It would require less boilerplate code and be better for performance if the mappings for this could be injected directly into SubChunkConverter.