Migrate SharedPreferences "Persistent" Storage to DataStore API

[epicstar]

SharedPreferences is deprecated. Let's instead use Jetpack's DataStore library, which replaces SharedPreferences.

To my knowledge, we only use SharedPreferences for store a user's most recent multi-selected routes to display.

We need to add a way to migrate from SharedPreferences to Datastore so that there is a seamless transition for the user.