Blender Git Loki

Fix #32198: UV unwrap of half a UV sphere would not give a perfect sphere as a
result. This wasn't really guaranteed anyway, because of numerical precision and
possible asymmetry in the triangulation, but we can do a bit better.

Now we bias the choice of how to split a quad into two triangles slightly
towards one of two possibilities, so that in case they are equal, floating point
errors do not decide the direction and symmetry is preserved.