Add a method to await a specific event

[gunnarmorling]

From Julien Viet: https://twitter.com/julienviet/status/1339523188301152262

There should be a method acting as barrier that a specific event (e.g. socket write) has happened.

[phejl]

I've briefly looked into this and it would need some clarification on the use case (as I don't want to make wrong assumptions). From my point of view options would be:

• Await for any matching event "in history" (so it won't wait if we have received an event or we will wait for it otherwise). One might use existing reset() to clear history.
• Await for an upcoming event from now where now would be a just the moment of the call - like a wall clock so events from the JFR might have happened a bit earlier if those were delayed.
• Await for an upcoming event after performing the sync through awaitEvents - more precise definition of "now" but likely tricky to implement.