Mods may change singlenode mapgen to generate stone,
in which case we want them to be able to also reenable
the standard mapgen_shared hooks.
- If def.enabled == true, always run the hook.
- If def.enabled == false, never run it.
- If def.enabled is not set (nil) then run it based on
standard logic, i.e. not on singlenode.
- Register def tables instead of bare funcs.
- Add labels for mod logic use.
- Automatically skip for singlenode mapgens,
e.g. for the skyblock modpack.
- Apply stratification last in shared mapgens, so it can see all
already-placed ores.
- Support stratification for nodes other than plain stone.
- Register lode stone and lode ore for stratification.
