Function withInsertedWaypoints

withInsertedWaypoints(
    route: Route,
    existingWaypoints: WaypointLike[],
    newWaypoints: WaypointLike[],
): WaypointLike[]
Returns a new array of waypoints with each new waypoint inserted at its optimal position.

The multi-waypoint variant of withInsertedWaypoint: it takes each new waypoint's slot from findBestWaypointInsertionIndices, and splices the new waypoints in along-route order, whatever their input order.
Parameters
- route: Route
  The existing calculated route, a Feature with LineString geometry.
- existingWaypoints: WaypointLike[]
  The existing waypoints in order, from origin through intermediate waypoints to destination.
- newWaypoints: WaypointLike[]
Returns WaypointLike[]
A new array with the waypoints inserted at their optimal positions.
Remarks
- Waypoints that project to the same location keep their input order.
- It returns a new array and leaves existingWaypoints unmodified.
- Passing an empty newWaypoints array returns a shallow copy of existingWaypoints.
- When the route has fewer than 2 coordinates or there are fewer than 2 existing waypoints, all new waypoints are prepended in input order.
Example
```
const waypoints: WaypointLike[] = [
  [4.9, 52.3],   // origin
  [5.0, 52.4]    // destination
];

const updated = withInsertedWaypoints(route, waypoints, [[4.97, 52.37], [4.93, 52.33]]);
// → [[4.9, 52.3], [4.93, 52.33], [4.97, 52.37], [5.0, 52.4]]
```