Entity Object Builders

[Platymemo]

This PR adds:

• A new library, entity identical to the one in #42
• Four new modules, entity, points_of_interest, vehicle and villager.
  • Each module provides helpers and builders to register their relevant values.

[OroArmor]

I believe that entity_types and entity_attributes are general enough to entities to be merged into a entity module. Similar to how the item library has the item module.

[OroArmor]

The real question is where something like the EntityRendererRegistry stuff should go, since that's both client and entity. Personally I think entity/entity (see above) is fine for it, as that's where it will most likely be used from, but it could be in other modules.

[Platymemo]

I believe that entity_types and entity_attributes are general enough to entities to be merged into a entity module. Similar to how the item library has the item module.

I went ahead and did that, I think it makes sense and it makes the javadocs play nicely

[Platymemo]

Sorry about the force-pushes, I rebased instead of merging and did a dumb and I won't be doing that again.

[oliviathevampire]

Could this be updated to 1.19.1? I think a lot of stuff is not needed longer