verse event subscription helper functions

https://dev.epicgames.com/community/learning/tutorials/woOK/fortnite-using-verse-fields-event-type-in-a-umg-user-widget

from the event UMG update. TODO: test if you can use this for events outside of UMG by just signaling the event or if you need extra sauce

subscription_helper.verse

# Custom event class to hold an Event, Cancel, and Await function
event_subscription := class:
    CancelEvent:event() = event(){}
 
    Cancel():void=
        CancelEvent.Signal()
 
# Async function that holds until the event is signaled or canceled
AwaitForEvent(Event:event(t), Callback(:t):void, Subscription:event_subscription where t : type)<suspends>:void=
    race:
        loop:
            # Await till event is signaled
            Payload := Event.Await()
            Callback(Payload)
        # Await till event is cancelled
        Subscription.CancelEvent.Await() 
 
# Call this function to subscribe to an event which spawns the AwaitForEvent async function to fire when the event is signaled
(Event:event(t) where t : type).Subscribe(Callback(:t):void):event_subscription=
    Subscription := event_subscription{}
    spawn{ AwaitForEvent(Event, Callback, Subscription) }
    return Subscription