handle transportables when splitting / joining train parts

[namdre]

• when joining, all transportables (persons & containers) should be part of the joint train
• when splitting, transportables should be moved to the train part according to their destination (same logic as with lines="ANY")
  • in case of ambiguity (both parts reach the intended destination) we could resolve this by schedule (use part with earlier arrival at destination)

This is basically a do-what-i-mean solution. For fine grained yard operations we would need something like #3874

[namdre]

intermodal router already handles splits/joins fine but the persons do have to do a change of trains which applies boardingDuration twice.

Since the train id may change in transit during split or join, it makes sense to have this as two distinct <ride> (or <transport>) elements in the output. However, boarding duration should not be applied.