Function convert_osm::split_ways::split_up_roads

pub fn split_up_roads(
    map: &mut RawMap, 
    input: OsmExtract, 
    timer: &mut Timer<'_>
) -> (Vec<(Pt2D, Amenity)>, HashMap<HashablePt2D, OriginalRoad>)

Returns amenities and a mapping of all points to split road. (Some internal points on roads are removed, so this mapping isn't redundant.)