Function convert_osm::split_ways::should_collapse_roundabout

fn should_collapse_roundabout(r: &RawRoad) -> bool

Many "roundabouts" like https://www.openstreetmap.org/way/427144965 are so tiny that they wind up with ridiculous geometry and cause constant gridlock.

Note https://www.openstreetmap.org/way/394991047 is an example of something that shouldn't get modified. The only distinction, currently, is length -- but I'd love a better definition.