Set the schedule we should be playing right now. Allows the NPC to start either a Lua schedule or an engine schedule. Despite sharing the same name as CAI_BaseNPC::SelectSchedule(), this isn't hooked to that function; this is called by Lua's ENTITY:RunAI, doesn't return an engine function, returning an engine function doesn't help and doesn't make the NPC start an engine schedule. To alter initial engine schedule, it is recommended to use ENTITY:TranslateSchedule.