Request: event-based DynamicElement

[juh9870]

It would be good to have a dynamic element that isn't updated every tick to check for condition, but rather listen to some event, and only triggers the rebuild function if a new value was emitted by that event. The main use case is to have DynamicElement that is tied to changes in some other field, without wasting resourced updating it every tick. Performance impact is negligible with one, but what about a dozen?