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.

lib/Slic3r/Test.pm

@@ -139,7 +139,6 @@ sub mesh {
     
     my $mesh = Slic3r::TriangleMesh->new;
     $mesh->ReadFromPerl($vertices, $facets);
-    $mesh->repair;
     $mesh->scale_xyz(Slic3r::Pointf3->new(@{$params{scale_xyz}})) if $params{scale_xyz};
     $mesh->translate(@{$params{translate}}) if $params{translate};
     return $mesh;