Fail less often for intersection geometry

Especially when we use raw OSM footways, we break on so many intersection geometry cases (the circles):

I'll start looking into these, but I've also been looking at how https://github.com/StrandedKitty/streets-gl handles things. It's much more robust.

TODO:

- [ ] Can we have an optional mode where we don't trim back road center-lines at all and have empty intersection polygons, just to debug and see how it looks?
- [ ] Investigate what streets-gl does and see if we can adapt ideas from it

CC @BudgieInWA in case you're interested or have ideas. osm2streets has revived thanks to the Muv work. I'm kind of interested in getting footways and crossings all showing up exactly as they're in OSM, and generally getting rid of the old inferred sidewalks mode.

Bei diesem Issue geht es um Fehler in der Schnittgeometrie bei der Verarbeitung von OSM-Fußwegen. Sieh dir den Code von osm2streets an, der Straßenmittellinien beschneidet und Schnittpolygone erstellt. Vergleiche ihn mit dem Repository streets-gl, um Ideen für eine robustere Implementierung zu erhalten. Beginne damit, einen optionalen Debug-Modus zu implementieren, der das Beschneiden deaktiviert, um die unveränderte Geometrie zu visualisieren.

Vom Indexierungsmodell aus dem Issue-Text verfasst.