fix 5156-new node Straight Skeleton Offset (External and internal mode)

[satabol]

Sverchok 1.3

fix #5156

[satabol]

If offset is internal (value is positive) the no problem:

All internal offsets do not intersects with contours of any other polygon or other words an internal offset do not out of outer boundary. It property help to parallelize computation.
But there is a problem if offset is external. It can overlapped with contours of external objects:

To fix this is an algorithm 3.2 at: https://doc.cgal.org/latest/Straight_skeleton_2/index.html

[satabol]

Additional Error if selected shape mode "Invert holes Soft/Hard":

Here is one hole but algorithm do two holes!

[satabol]

[satabol]

Invert Holes work Good: