Pair IndirectSectionRef with single types (apply through model)

[skinkie]

In IndirectSectionRef there is a construct that would allow building pairs of StopPoint, StopPlace and Quay to match a specific section, also when it is not matched exactly to the timetable via StopPoint. I want to propose we limit this to a pair of a single type. Hence change the choice structure.

StopPoint-StopPoint
StopPlace-StopPlace
Quay-Quay

But not variants like:
StopPoint - StopPlace
StopPlace - Quay.

https://github.com/TransmodelEcosystem/SIRI/blob/v2.2/xsd/siri_model/siri_situationAffects.xsd#L673