An upgrade to river and lake biomes using the new 3D biome format.

Caves & Cliffs introduces the first proper use of the 3D biome format. This is how we can get cave biomes beneath current biomes and the new mountains to generate.

However I feel like an upgrade to the overworld which changes all the current biome generation for the overworld is long overdue, since yes they will utilise the 3D biome format in 1.18 - they won't look any different.

What I mean by an upgrade is to allow things such as lakes and hills to freely exist together to create natural valleys, rivers and lakes which are height-dependant, since those right now all generate at the same level and we don't get naturally-generated lake/river-to-waterfall style generation which I think would vastly improve the water generation in the overworld.

For example, a Giant Tree Taiga hills biome can have a river run through it, but at a higher altitude which instead of the river getting cut off, it can create a waterfall which flows down to the lower area once the hills stop.

A lot of people have been asking for waterfalls and actual rivers which I think now is the perfect time to add these since the 3D biomes are the answer to these hurdles and will allow more natural river and lake generation.