This reverts commit 627d8bcaefb3c46864324554f663403495d9ef43, reversing
changes made to 66d44627248b8e412143298541b5a8397f8a0af5.
The change breaks build on mac
limited anchors, while before a full perimeter segment was always
taken if possible.
2) Adapted the line infills (grid, stars, triangles, cubic) to 1).
This also solves a long standing issue of these infills producing
anchors for each sweep direction independently, thus possibly
overlapping and overextruding, which was quite detrimental
in narrow areas.
3) Refactored cubic adaptive infill anchroing algorithm
for performance and clarity.
Implementation of 2-opt pairwise exchange iterative improvement
algorithm with an extension to a chain of segments, where
the chain of segments may get flipped during the exchange operation.
The 2-opt exchange algorithm may be quite slow.
