[buffer] remove RobustPolicy from side_on_convex_range
because side of a point w.r.t. a segment cannot be done with rescaling,
due to rounding the point can be located on the other side of the segment
This adds 4 more failing testcases, but it has to be done first because
the solution is not reliable
[buffer] merged implementations of side_on_convex_range
[buffer] use intersection_side for checking side on convex range
This fixes many of the issues (in multi_polygon_buffer). However, some
new cases now fail because of this and should be fixed later