GDExtension for 3D Gen

I turned the 3D example into a GDExtension. Sample project is included, as well as just the extension itself. The extension works by making landscape “chunks”.

* The row and column settings allow you to choose how many chunks are made.
* Indices distance is the distance between indices in the created mesh.
* Max height is the maximum height of the landscape
* Height exponent sets max height to the power of this value
* Detail is how the noise is scaled to the landscape
* There's an option to generate navigation on the procedural mesh as well
* Terrain material is the material to apply to the landscape
* Noise Texture allows you to set the noise that will be used for generation