Change reroute radius threshold calculation

[bsudekum]

We've had reports of constant rerouting on highways. Our current thinking that this is a combination of a few factors:

• user has very high gps accuracy
• user is traveling on large highway with many lanes
• user has high horizontal distance from the route geometry (I.E. in first lane)

These combinations could produce a rerouting event since their horizontalAccuracy is < 10m and the RouteControllerUserLocationSnappingDistance is `10m. This produces a radius threshold of only 20m.

This change now looks at the maximum value between RouteControllerMaximumDistanceBeforeRecalculating (50m) and the horizontalAccuracy + RouteControllerUserLocationSnappingDistance (10m).

Here are the situations that will change:

• 👍 fewer rerouting on a highway with good accuracy
• 👎 possibly longer time to reroute while in urban areas (with worse horizontal accuracy)

/cc @mapbox/navigation @danpat @willwhite

[bsudekum]

In f2c9e69, I changed when we snap. Previously we:

• if snapping was enabled, we always returned a snapped location
• even if we errored while calculating the snapping course, we still returned a snapped location
• if a user was not snapped, we rerouted

Now:

• if anything errors while calculating the snapped location or location we return a non snapped location
• We check if the snapped location is greater than RouteControllerUserLocationSnappingDistance, we return the users actual location and course
• This allows for more wiggle room and less aggressive snapping and rerouting

[bsudekum]

@frederoni @1ec5 after testing this for a bit, I think it's makes for a good addition. 👍 on merging?