Draconghost/Terrain3D ? reverse-engineered prompt

Build me a Godot 4 terrain addon that lets me create and edit huge outdoor maps without the game bogging down.

I want it to work as a native extension so it can be used from Godot without needing a custom engine build, and I want to be able to use it from GDScript and C# too. It should support large terrains made of separate regions, with smooth level of detail so it stays fast, plus sculpting tools, holes, texture painting, detiling, color painting, and wetness painting. It should also handle foliage placement with its own detail levels and a simple shadow impostor for performance.

Please include a way to import heightmaps from common terrain tools, and make sure the setup is easy to understand from the editor. If anything important is missing, please check the current docs online and follow the project’s existing style.