trip_id not provided for blocks with reoccurring stop_ids

[barbeau]

Summary:

If a GTFS block contains multiple references to the same stopId (i.e., the bus visits the same stopId more than once in the same block), but in different trips, then in the GTFS-rt data the tripId for each TripUpdate.TripDescriptor must be provided. If not, this is an error. In this case, the bus wouldn't visit the same stopId more than once in the same trip.

This is currently defined as E008 in ValidationRules but is not implemented.