Replaced several core classes from DD with new classes to enforce
integrity checks. Rewriting everything that depended on those classes is
a massive undertaking but it should simplify our code and prevent the
many bugs we've seen lately. The rewrite isn't done yet, just committing
my progress so far.
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.
