Created NewLinkData and replaced references to the original LinkData.
Moved it to the mod_pocketDim.core package. Added Point4D, an immutable
point type for 3D integer coordinates with an added dimension ID.
Renamed MobObelisk to MobMonolith. Renamed LimboSkyProvider and
PocketProvider to have Xs at the ends of their names. This is temporary
so that I can change the name's capitalization. Windows considers the
names the same because it's file naming is case insensitive.
