Iterates through the path one step at a time. Each step consists of an object containing a
vertex, and, for all entries except the first, an
edge member, which supplies the Edge that links to the Vertex (which is why it is null for the first entry).
each(fn: (i: number, p: ShortestPathComponent) => any): void;
|fn||(i: number, p: ShortestPathComponent) => any||Function to call for each step.|