Better healing for Glyph shape - remove duplicit points + self intersections

Add search of intersecting points (compared with CGAL)
Triangulation can [optionaly] accept multi points

src/libslic3r/Point.cpp

@@ -158,6 +158,24 @@ bool has_duplicate_points(std::vector<Point> &&pts)
     return false;
 }
 
+Points collect_duplications(Points pts /* Copy */)
+{
+    std::stable_sort(pts.begin(), pts.end());
+    Points duplicits;
+    const Point *prev = &pts.front();
+    for (size_t i = 1; i < pts.size(); ++i) {
+        const Point *act = &pts[i];
+        if (*prev == *act) {
+            // duplicit point
+            if (!duplicits.empty() && duplicits.back() == *act)
+                continue; // only unique duplicits
+            duplicits.push_back(*act);
+        }
+        prev = act;
+    }
+    return duplicits;
+}
+
 BoundingBox get_extents(const Points &pts)
 { 
     return BoundingBox(pts);