Add waypoint indices option for Directions API

[1ec5]

The Directions API will soon expose a waypoints parameter similar to the Map Matching API’s: Project-OSRM/osrm-backend#5345. To support it, we could move MatchOptions.waypointIndices and its support code to DirectionsOptions, allowing RouteOptions to inherit it:

https://github.com/mapbox/MapboxDirections.swift/blob/c350b60489c33845551cf0163a5481d32c940479/MapboxDirections/Match/MBMatchOptions.swift#L49-L56

However, this would be a good opportunity to replace the parallel index set with a more object-oriented property on Waypoint that determines whether the individual waypoint is explicitly persisted in the route response. I’m not sure what to name it: isPersistent? isIncludedInCalculatedRoute? isRepresentedByArrivalAndDepartureSteps? separatesTwoLegs? isIncludedInInstructions? isImpliedByCalculatedRoute? isViaPoint?

Based on this property, we’ll have to revisit the assumption that RouteOptions.waypoints lines up with the response’s waypoints:

https://github.com/mapbox/MapboxDirections.swift/blob/c350b60489c33845551cf0163a5481d32c940479/MapboxDirections/MBRoute.swift#L27-L29

/cc @mapbox/navigation-ios @danesfeder

[1ec5]

@JThramer suggested a WaypointType enumeration with the values .stop and .via. The enumeration values will need to make sense for both RouteOptions and MatchOptions.

[1ec5]

mapbox/mapbox-navigation-android#875 and mapbox/mapbox-java#956 track the equivalent for Android.