code came from #6015 and will be subject to probable changes

An asynchronous event is one that allows the addition of promises to be resolved before being completed.
This implementation integrates priority levels, allowing you to wait for all promises added to one level before moving on to the next.
This is made possible by separating the event call logic into several functions, which can then be integrated into AsyncEventTrait::callAsync()

If the event is async and the handler return Promise, it will be handle as an async event.
However, if the event is async and the handler return smth different than Promise, it will be handle synchronously.
An async handler can specify if it wishes to be called with no concurrent handlers with the tag @noConcurrentCall

Co-authored-by: Javier León <58715544+JavierLeon9966@users.noreply.github.com>

… AsyncEventDelegate

…anager function

…ents