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.
Using a positive curvature estimate to control the strength
of the Elephant foot compensation shall work similarly to
the previous implementation while avoiding pinching off
tiny pieces from the contour.
by @supermerill and @wavexx
WIP: The function Fill::connect_infill() is being rewritten
to utilize spatial structures wherever possible for lower CPU load
and less dynamic memory allocation.
