Some touchups in fix self-intersect.
Some touchups in fix self-intersect.

Grid is not _much_ faster (if at all) but at least the loops are easier to read now. Turns out removing the debug code and compiling in release mode got the speed back to reasonable values anyway. Also decided not to imporve on the 4x application of simplify-polygons since I know this at least works and the cost is neligable compared to the 'compare all lines to all points' that needs to be done in the 2nd part of the function.

CURA-7562

Ultimaker/CuraEngine,Ultimaker/CuraEngine