Add cardinal direction field to some route presets

[1ec5]

Added a Direction field to the Cycle Route, Road Route, and Train Route presets (and by extension other public transportation route presets). The field has only been added to route relation types that are commonly tagged with cardinal directions as of writing; I didn’t find enough usage on hiking, horse, or piste route relations to justify matching 9f092d8.

Unlike the other Direction fields, this is a combo box that suggests cardinal directions. Both the N/S/E/W and north/south/east/west formats are approved and well-established overall, but the latter predominates among route relations, so that’s what this PR introduces. The combo box allows user-defined values, since public transportation systems use a variety of idiosyncratic rail directions, some of which are commonly tagged in OSM.

Fixes #202.

[tyrasd]

I don't know. Currently, only very few relations use this tag (see below). The wiki only mentions usage for some specific countries: Perhaps it would make more sense to limit this to road route relations in the US, Canada and New Zealand for now?

route type	total count	count with direction	relative amount
route=bicycle	87007	65	0.07%
route=train	11038	42	0.4%
route=road	197179	1413	0.7%
route=road (USA only)	48912	661	1.4%

[1ec5]

I limited the field to the three MUTCD countries where routes are commonly identified by cardinal direction. There’s no real-world justification for limiting it to just road routes in these countries, because bicycle and public transportation routes are commonly referred to in the same way. There’s more information in this wiki page, which has presented the direction tag as one of two approaches for many years.

[tyrasd]

because […] public transportation routes are commonly referred to in the same way.

Then why not also add route=bus, route=subway, route=tram and route=light_rail as well? 🤔

Perhaps the non-road route types could instead have the field in the moreFields section?

[1ec5]

So far, I’ve only added cardinal directions to this field. For public transportation routes that distinguish directions, there’s more local variation, like “inbound” versus “outbound”, so I wasn’t sure about broaching that here. By contrast, long-distance bike routes are always referred to by cardinal directions in the U.S. (not sure about Canada and New Zealand).

I agree that we could add the field to moreFields for the public transportation presets just in case a local community finds it suitable for their local bus or subway system. The original motivation for this PR was that iD is already using direction for its automatic relation labels, so I guess it would be more consistent to add it to all of them.