LOD is biased when walking on a high mountain or deep valley

[Zylann]

LOD is distance-based, but the distance from "sea-level" is also taken into account, as a result if you sit on top of a mountain, that mountain won't have max LOD because your distance from sea-level is high. LOD should use the actual height as reference. (just ignoring altitude wouldn't work because you could be flying)

Also the 0.5 addition to target the center of a chunk seems to be wrong too https://github.com/Zylann/godot_heightmap_module/blob/master/quad_tree_lod.h#L175 Because origin is scaled already