Function S2Polygon.getLastDescendant

Return the index of the last loop that is contained within loop k. Returns num_loops() - 1 if k < 0. Note that loops are indexed according to a preorder traversal of the nesting hierarchy, so the immediate children of loop k can be found by iterating over loops (k+1)..GetLastDescendant(k) and selecting those whose depth is equal to (loop(k)->depth() + 1).