Fix TriggerBase entity list bug. Entities with multiple colliders could get into the following situation: - Collider A enters the trigger. The base entity is added to the entityContents HashSet. - Collider B enters the trigger (same entity). - Collider A leaves the trigger. The base entity is removed from the entityContents HashSet. But the entity's Collider B is still in the trigger. This fix keeps the entity around until all colliders on it have left the trigger.