Petra: assign guards to the hero in regicide games
Summary:
Petra will assign military units as guards to the hero in the regicide victory condition, preferring any available Champion units.

Also this diff fixes a broken loop through a Map in D140/rP19226 that was introduced when switching criticalEnts.guards from a Set to a Map.

Patch by Sandarac

Differential Revision: https://code.wildfiregames.com/D157