Initial implementation of MeshClipper class

So far the work is shared between the old code in GLGizmoSlaSupports.cpp and the new class

src/slic3r/GUI/MeshClipper.hpp

@@ -0,0 +1,37 @@
+#ifndef slic3r_MeshClipper_hpp_
+#define slic3r_MeshClipper_hpp_
+
+#include "libslic3r/Point.hpp"
+#include "slic3r/GUI/GLCanvas3D.hpp"
+
+namespace Slic3r {
+namespace GUI {
+
+class MeshClipper {
+public:
+    void set_plane(const ClippingPlane& plane);
+    void set_mesh(const TriangleMesh& mesh);
+    void set_transformation(const Geometry::Transformation& trafo);
+
+    const std::vector<Vec2f>& get_triangles();
+
+private:
+    void recalculate_triangles();
+    std::pair<Vec3f, float> get_mesh_cut_normal() const;
+
+
+    Geometry::Transformation m_trafo;
+    const TriangleMesh* m_mesh = nullptr;
+    ClippingPlane m_plane;
+    std::vector<Vec2f> m_triangles;
+    bool m_triangles_valid = false;
+    std::unique_ptr<TriangleMeshSlicer> m_tms;
+};
+
+
+    
+} // namespace GUI
+} // namespace Slic3r
+
+
+#endif // slic3r_MeshClipper_hpp_