Improve terrain generation

[BarthPaleologue]

With WebGPU compute shaders, all terrain generation code will be rewritten, which is the perfect occasion to improve its quality.

Here are some ideas that could be used:

• Some domain warping https://wwwtyro.net/2017/04/03/cursive-noise.html
• Nice erosion noise https://www.shadertoy.com/view/MtGcWh and https://www.shadertoy.com/view/7ljcRW
• Terraces and canyons https://gamedev.stackexchange.com/questions/116205/terracing-mountain-features

[BarthPaleologue]

The analytic normal will be abandonned in favor of erosion by gradient division.

This will also make it easier with craters (3d worley)

Domain warping can bé used for biome blending.