Visits all pairs of crossing edges in the given S2ShapeIndex, terminating
early if the given EdgePairVisitor function returns false (in which case
VisitCrossings returns false as well). "type" indicates whether all
crossings should be visited, or only interior crossings.
Visits all pairs of crossing edges in the given S2ShapeIndex, terminating early if the given EdgePairVisitor function returns false (in which case VisitCrossings returns false as well). "type" indicates whether all crossings should be visited, or only interior crossings.
CAVEAT: Crossings may be visited more than once.