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

[ianthetechie]

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:

• Support Polyline insertion relative to a specific layer ID Rallista/maplibre-compose-playground#85 - Blocker for supporting this on Android.
• Support layer insertion below all labels maplibre/swiftui-dsl#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