Fixes Solid infill where there should be none #6482
Also the safety offsetting was revised to be enabled only where needed,
the "do safety offset" is now easy to discover by
a new ApplySafetyOffset::Yes enum, and safety offset over union, which
is better done by offset() / offset_ex() has been replaced with
new union_safety_offset() / union_safety_offset_ex() functions, which
better convey their meaning and which could be better optimized than
union() with the safety offset applied.
Fixed some old support and infill issues.
Fixes support problem #4295
Fixes Parts of interface layer extends beyond supports and cannot be printed
Fixes support missing under horizontal overhang #6058
Fixes Slicer double-traces small sections of Rectilinear Supports, causes
Fixes plastic buildup and nozzle crashes #4951
Fixes Add "Angle Interface layers" #2969
