Framework and implementation for additional placement states for certain blocks
Features:
- no added items - additional placements are extensions of the existing slab and stair block placement logic
- supports slabs and stairs (vertical) and carpet and pressure plates (on walls and ceiling)
- vertical stairs actually connnect to other stairs (and vice-versa)
- supports most modded blocks
- simple datagen helpers to generate blockstates, block models, and item models for modded blocks, in case extra compatibility is needed