Stick to similar alternative route when re-routed

[kmadsen]

Steps to reproduce

1. Request a route with alternatives
2. Select an alternative (not the fastest)
3. Drive off route
4. Stay on route similar to the original alternative

References to similar issues

Legacy feature request #764
Algorithm investigation #3116
Conclusions for comparing routes for Faster Route, route compare #3301

[1ec5]

As noted in mapbox/mapbox-navigation-ios#3598, sometimes the user doesn’t want to preserve their original selection. Since we can’t automatically know the user’s intent when they deviate from the route, the UI can offer the user a way to explicitly switch to a different route, “unsticking” from the original selection.

[1ec5]

Per mapbox/mapbox-navigation-ios#3597 (comment), any route similarity heuristic, whether based on names or geometry, should also have a minimum similarity threshold. It’s important to avoid situations where a completely different route gets selected over a more optimal route just because of nominal similarity to the original selection.