OSM and other raw input into and store, before later converting to a
Map.
Why?
- build-time performance: while iterating on geometry problems, map_editor in release mode took 33s to build before, 11s now that the crate is split
- better layering: operations on a RawMap are becoming increasingly distinct from later transformations on the bigger map model
- this helps tease apart the dependencies of the intersection polygon algorithm for #846
- this will make it simpler to cutover to osm2lanes for https://github.com/a-b-street/osm2lanes/issues/71
There's further reorganization in raw_map and map_model that'll follow,
but the main work is done here.
