Lots of improvements to MotionPlanner/avoid_crossing_perimeters. Smoother paths and several edge cases now handled better

xs/src/libslic3r/MotionPlanner.hpp

@@ -33,10 +33,14 @@ class MotionPlanner
     
     void initialize();
     MotionPlannerGraph* init_graph(int island_idx);
+    ExPolygonCollection get_env(size_t island_idx) const;
+    Point nearest_env_point(const ExPolygonCollection &env, const Point &from, const Point &to) const;
 };
 
 class MotionPlannerGraph
 {
+    friend class MotionPlanner;
+    
     private:
     typedef size_t node_t;
     typedef double weight_t;