Reimplement RouteProgress based on navigator status

Nobody has claimed this yet.

MapboxNavigationNative provides route progress statistics, but RouteController mostly ignores it in favor of the calculations in RouteProgress. At some point, we may want to migrate over to MapboxNavigationNative’s calculations for consistency.

MapboxNavigationNative ensure a consistent Earth radius or distance formula between MapboxNavigationNative and Valhalla. Currently, Core Navigation calculates and aggregates route progress statistics purely from the fields coming from the Directions API, which ensures consistency with the API whether the endpoint happens to be powered by Valhalla or OSRM (which may use different constants). Differences in Earth radius and distance formula have bitten us in the past, and there’s still some inconsistency on the client side: mapbox/turf-swift#26. Migrating to MapboxNavigationNative for this purpose will be a bit sad because RouteProgress is such a showcase for Swift functional programming – especially compared to the C++ that would replace it under the hood.

/cc @mapbox/navigation-ios

Start by reading RouteController and RouteProgress, then compare their current calculations with the route progress statistics provided by MapboxNavigationNative. Review the consistency concerns involving the Directions API, Valhalla, OSRM, and turf-swift#26. Done means RouteProgress is reimplemented around navigator status with consistent progress calculations.

Written by the indexing model from the issue text.