Move arrange polygon in Polygon_2

[sloriot]

The following file:
Straight_skeleton_2/include/CGAL/arrange_offset_polygons_2.h

contains the 2D equivalent of the function PMP::orient_to_bound_a_volume() and IMO, it should be moved in the Polygon_2 package as it will increase its visibility (someone even asked for it on Stackoverflow and I did not know this function existed).

[sloriot]

I think there is somehow an equivalent functionality here

[maxGimeno]

The file arrange_offset_polygons_2.h specifies in a comment that the functions only work with polygons created with the Polygon_offset_builder, that must be why it is in Straight_skeleton.

[maxGimeno]

The preconditions for the function are:

• Polygons are simple
• Outer polygons are CCW while holes are CW
• Outer polygons do not contain other outer polygons, only holes
• Every hole is contained in one and only one outer polygon
  It seems a little heavy for a Polygon_2 function IMHO