vanilla datapack missing world generation options

PROBLEM:
The world_gen, dimension, and dimension_type folders are missing from the vanilla datapack.

TO REPRODUCE:
Open the client jar (.minecraft/versions/21w11a/21w11a.jar)
Navigate to the vanilla datapack (data/minecraft)

EXPECTED RESULTS:
It is expected to see the world_gen, dimension, and dimension_type folders

ACTUAL RESULTS:
The world_gen, dimension, and dimension_type folders are missing.

FIX:
Add them to the datapack, instead of hardcoding them.

REASONING:
This is useful for people working with datapacks doing world gen modifications. It allows them to see the format and defaults for the vanilla world gen settings and clone and modify them as needed.