The function nearest_neighbor is the function template version of the nearest neighbor search on Delaunay
nearest_neighbor ( Dt delau, Dt::Vertex_handle v)
computes a handle to a vertex of that is closest to .
If is the only vertex in , is returned.
Dt is a CGAL Delaunay triangulation and contains the following subset of types from the concept PointSetTraits and from
the Delaunay triangulation data type: