Default overlays near maneuver points

I don't think this is high priority until someone comes along with an opinion / need for it, but creating the issue anyways. We theoretically already enable the user to add overlays (we allow arbitrary customization of the map via builders on both iOS and Android). But _most_ navigation experiences have some sort of overlay like a white line (MapLibre Navigation, Organic Maps), a "pin" with a maneuver sign (can't remember where, but I've definitely seen this somewhere), etc. I assume we'll want to offer one that's reasonable out-of-the-box eventually.

Some examples:

MapLibre Navigation


Organic Maps

The issue names no files, tests, or entry points. Start by reviewing the existing iOS and Android builder APIs for map customization and how maneuver points are exposed. Done requires an agreed default overlay design and verification that it works on both platforms.

Written by the indexing model from the issue text.