Fix of "Variable layer height feature breaks after rotating part #2073"

There was an approximate bounding box used at the GUI, while a snug
bounding box was used at the back end, causing invalidation
of the variable layer height editing profile on rotated objects.

A snug bounding box around the first instance is now cached.

src/libslic3r/Print.hpp

@@ -132,7 +132,7 @@ public:
     // The slicing parameters are dependent on various configuration values
     // (layer height, first layer height, raft settings, print nozzle diameter etc).
     const SlicingParameters&    slicing_parameters() const { return m_slicing_params; }
-    static SlicingParameters    slicing_parameters(const DynamicPrintConfig &full_config, const ModelObject &model_object);
+    static SlicingParameters    slicing_parameters(const DynamicPrintConfig &full_config, const ModelObject &model_object, float object_max_z);
 
     // returns 0-based indices of extruders used to print the object (without brim, support and other helper extrusions)
     std::vector<unsigned int>   object_extruders() const;