Bind platform_edge to stop_area through platform membership

[alexey-zakharenkov]

There occur situations when a multipolygon platform that contain platform_edges as outer lines belongs to a stop_area, but a platform_edge is included into the route. That is, if an arrow designates "is included into relation" relationship, the diagram is

station ---> stop_area <--- platform <--- platform_edge ---> route

which results in "platform [reference to platform_edge] is not connected to a station in route" error. I propose to recognize such transitive inclusion of platform_edges into stop_areas.

[Zverik]

When I fixed subway networks, I added these platform edges into stop_area relations directly. The reason for that is not overcomplicating the tagging schema. This subway validator is de-facto installing the rules for mapping subways. If we say that any member of any relation inside a stop_area also belongs to a stop_area, we would make any other consumer parsing the data implement this.

It would help to detect and display such cases as errors, but I'm really not sure about supporting these.