Currently every routing wrapper implements the virtual Wrapper::add_route_info function to populate the route geometry and the routes[].steps[].distance values in output. This means the same logic is duplicated in various files to populate the distances, with small subtle differences depending on the underlying routing engine.

Once we have #956, we should be able to simply populate Step::distance values during the solution formatting process just as for Step::duration. Then we could turn the various *::add_route_info to much simpler *::add_geometry functions.