Ported encloses_point() to XS and renamed to contains_point()

xs/xsp/ExPolygon.xsp

@@ -22,6 +22,7 @@
     double area();
     bool is_valid();
     bool contains_line(Line* line);
+    bool contains_point(Point* point);
 %{
 
 ExPolygon*

xs/xsp/Polygon.xsp

@@ -33,6 +33,7 @@
     bool is_valid();
     Point* first_point()
         %code{% const char* CLASS = "Slic3r::Point"; RETVAL = THIS->first_point(); %};
+    bool contains_point(Point* point);
 %{
 
 Polygon*