naive-seamless-terrain for Godot(4.*)

• This is a slow, GDScript based Terrain system with "seamless" LOD borders.
• The method used to avoid seams is pretty naive, it doesn't attempt to blend mesh shapes or match topology, it simply ensures edge vertices that do not align with a neighbouring Patches own vertices(of a different subdivision) are linearly interpolated so that it sits flush with that neighbours edge elevation.
• Add a lod_patch.gd script to MeshInstance3D Nodes that are spaced 1x1 unit apart.
• Call do_lod with a Vector3 argument to generate a LOD for the distance to that Vector3.
• Tweak max_detail in lod_patch.gd to control max subdivision.
• Set elevation_function to your own Callable that accepts x and z as arguments and returns a float value representing elevation.
• Don't use this.