Fix: Merge duplicate points and orient polygons before triangulation to prevent invalid meshes

[hihry]

Fix: #8962 Clean polygon soup before triangulation

• Merge duplicate points to avoid degenerate vertices
• Orient polygon soup for consistent face winding
• Prevents invalid meshes and triangulation failures in
  make_conforming_constrained_Delaunay_triangulation_3()

[lrineau]

I do not think we can merge this pull-request. The preprocessing has to be done in a preprocessing step, and not in that function. If the user already as done some sort of preprocessing, that would be a waste of computation time to do it again.

Closing now.