RouteRequestGenerator implementation for Valhalla map matching

Today Ferrostar supports map matching, but requires a bit of extra development effort. Convenience methods / `FerrostarCore` constructors that support the Valhalla map matching request format would improve this.

This should be pretty trivial; it's just a slightly different request format. The response is the same.

Locate the existing map-matching request generator and FerrostarCore constructors, then compare their request format with Valhalla's format. The work is done when convenience methods or constructors accept Valhalla map-matching requests while producing the existing response type.

Written by the indexing model from the issue text.