Mesh intersection: coplanar facets on same side of radial edge in radial sort

[BrunoLevy]

$  intersect three_cubes.obj remove_internal_boundaries=true

fails (just keeps a couple of triangles instead of only removing the internal boundaries) where three_cubes.obj is here

There are duplicated triangles after mesh intersection. So the global vertex map / the comparison function might be bugged ? nope (see below)

• problem is still there with generic (slower) comparison function
• problem is there with both expansion_nt and exact_nt
• fast path (on signs) in ratio_compare() ? Nope (problem still there when commenting-out)

[BrunoLevy]

gotcha red vertex exists as an original vertex of A, and as an intersection between an edge of B and an edge of C

[BrunoLevy]

Added post-processing loop that queries the global vertex map with all existing vertices and that merges them in case of a match.