AutoPlacement event flows

AutoPlacement event flows are used by the AutoPlacementMgr to determine whether actors should be dynamically spawned without having to hardcode special logic into the executable.

Such event flows are executed by the same event flow engine but with a different environment: only the "AutoPlacement" pseudo-actor is available for actions and queries, and subflows do not appear to be usable^[check]. Actions and queries are not mapped to AI system functions as with regular event flows, but are entirely handled by the AutoPlacement code.