Blender Git Loki

Fix T47564: Unwrapping the same mesh results in different UVs.

Pointers of faces were passed as face keys during parametrizer's face creation. Since those
addresses were different for every run, the layout of the faces ended up being different
in the internal hash, leading to inconsistent order of their evaluation during LSCM solving,
and slightly different UV maps.

Solved by simply using faces' indices as key instead, which ensures we always get same results
with exact same input data now.

Many thanks to Roman Nagornov (RomanN) for raising the issue, investigating it and finding
the solution! And thanks to Brecht for quick review too.