Invoke the method to update rendered maneuvers with road shields.
The provided shields are mapped to IDs of PrimaryManeuver, SecondaryManeuver, and SubManeuver and if a maneuver has already been rendered via renderManeuvers, the respective shields' text will be changed to the shield icon.
Invoking this method also caches all of the available shields. Whenever renderManeuvers is invoked, the cached shields are reused for rendering.
the map of maneuver IDs to available shields