This allows `lexicographical_topological_sort` and `TopologicalSorter`
to produce a topological sort that would have been found if the edges in
the graph had reversed directions, without constructing the edge-flipped
graph.

This is useful for graphs where we might want to do topological analysis
from both ends of the data flow, for example in Qiskit where we
occasionally want to find the "final" operations topologically.