Fixes scars on thing walls when "avoid crossing wall" is turned on (#…

…2659)

* Travel very close to the inner holes, could cross external perimeter when the avoid crossing perimeters was enabled.

(cherry picked from commit prusa3d/PrusaSlicer@6c51e51)

* Modified variable offset in the avoid crossing perimeters to not cause scars on thin objects (#7699).

Previously, the minimum contour width was chosen too conservative and, on some thin objects, only allowed minimal (or non) offset. This could result in travels being planned along the outer perimeter.

Now, the minimum contour width is chosen much smaller at the start and tested if the variable offset wasn't failed (the outer contour broke up into more parts, more or fewer holes, etc.).
If any problem is detected, the variable offset is recalculated with a larger minimum contour width.

(cherry picked from commit prusa3d/PrusaSlicer@dc00f0b)

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Co-authored-by: Lukáš Hejl <[email protected]>