Surface Mesh Approxination, non documented variables

[albert-github]

When generating the documentation with GENERATED_XML=YES we get the warnings:

.../Surface_mesh_approximation/include/CGAL/Variational_shape_approximation.h:1531: warning: The following parameter of CGAL::Variational_shape_approximation::find_edges(const FT subdivision_ratio, const FT boundary_subdivision_ratio, const bool relative_to_chord, const bool with_dihedral_angle) is not documented:
  parameter 'boundary_subdivision_ratio'
.../Surface_mesh_approximation/include/CGAL/Variational_shape_approximation.h:1853: warning: The following parameter of CGAL::Variational_shape_approximation::subdivide_chord(const Boundary_chord_iterator &chord_begin, const Boundary_chord_iterator &chord_end, const FT subdivision_ratio, const FT boundary_subdivision_ratio, const bool relative_to_chord, const bool with_dihedral_angle) is not documented:
  parameter 'boundary_subdivision_ratio'

in the "normal" documentation run we don't see these messages.

[sloriot]

Note that these are in private function so they shouldn't be reported. I fixed them nonetheless.

[albert-github]

Closed as completed by #8555