Fix of Random placment of top fill throughout model #7442

For this particular model, ClipperLib numerical instability causes
one of the internal surfaces to turn into bridging surfaces
on reslicing. The issue was fixed by reverting to untyped slices if possible.

src/libslic3r/Layer.hpp

@@ -137,6 +137,8 @@ public:
     //FIXME Review whether not to simplify the code by keeping the raw_slices all the time.
     void                    backup_untyped_slices();
     void                    restore_untyped_slices();
+    // To improve robustness of detect_surfaces_type() when reslicing (working with typed slices), see GH issue #7442.
+    void                    restore_untyped_slices_no_extra_perimeters();
     // Slices merged into islands, to be used by the elephant foot compensation to trim the individual surfaces with the shrunk merged slices.
     ExPolygons              merged(float offset) const;
     template <class T> bool any_internal_region_slice_contains(const T &item) const {