Eradicated admesh from TriangleMesh:

TriangleMesh newly only holds indexed_triangle_set and
TriangleMeshStats. TriangleMeshStats contains an excerpt of stl_stats.
TriangleMeshStats are updated when initializing with indexed_triangle_set.

Admesh triangle mesh fixing is newly only used when loading an STL.
AMF / 3MF / OBJ file formats are already indexed triangle sets, thus
they are no more converted to admesh stl_file format, nor fixed
through admesh repair machinery. When importing AMF / 3MF / OBJ files,
volume is calculated and if negative, all faces are flipped. Also
a bounding box and number of open edges is calculated.

Implemented its_number_of_patches(), its_num_open_edges()
Optimized its_split(), its_is_splittable() using a visitor pattern.

Reworked QHull integration into TriangleMesh:
    1) Face normals were not right.
    2) Indexed triangle set is newly emitted instead of duplicating
       vertices for each face.

Fixed cut_mesh(): Orient the triangulated faces correctly.

src/slic3r/Utils/FixModelByWin10.cpp

@@ -402,6 +402,7 @@ bool fix_model_by_win10_sdk_gui(ModelObject &model_object, int volume_idx, wxPro
 			}
 			for (size_t i = 0; i < volumes.size(); ++ i) {
 				volumes[i]->set_mesh(std::move(meshes_repaired[i]));
+				volumes[i]->calculate_convex_hull();
 				volumes[i]->set_new_unique_id();
 			}
 			model_object.invalidate_bounding_box();