Move the route polyline rendering below labels (and other symbols?)

One of our users pointed out that the route line obscures road labels. As far as I can recall, most other navigation maps will draw the polyline under all labels, so we should probably do this by default.

Related issues:

* https://github.com/Rallista/maplibre-compose-playground/issues/85 - Blocker for supporting this on Android.
* https://github.com/maplibre/swiftui-dsl/issues/69 - We can already do this today on iOS, but not in a style-neutral way. Ideally we try to do a smart insertion below all symbol layers since that's what almost everyone wants AFAIK