Lay flat gizmo improvements - merge adjacent faces, compute and cache convex hull for entire ModelObject, refresh when moved, etc.

xs/src/slic3r/GUI/GLCanvas3D.hpp

@@ -383,7 +383,7 @@ public:
         float get_angle_z() const;
         void set_angle_z(float angle_z);
 
-        void set_flattening_data(std::vector<Pointf3s> vertices_list);
+        void set_flattening_data(const ModelObject* model_object);
         Pointf3 get_flattening_normal() const;
 
         void render(const GLCanvas3D& canvas, const BoundingBoxf3& box) const;