Slabs

- [ ] Diorite and variants
- [ ] Andesite and variants
- [ ] Granite and variants
- [ ] Stone and variants
- [ ] Cobblestone and variants
- [ ] Ensure that single slabs of both heights work correctly
- [ ] Ensure that double slabs work correctly
- [ ] Ensure that recipes match Vanilla recipes
- [ ] Ensure no crashing or bad behavior when mixing varieties
