Special case `EventLoopPromise.succeed()` when `Value` is `Void`

[glbrntt]

To succeed an EventLoopPromise<Void> users must pass a void-value to it, e.g.:

• promise.succeed(())
• promise.succeed(Void())

It would be nice if we could spell this as promise.succeed().

[mob-connection]

Maybe something like this ?

extension EventLoopPromise where Value == Void {
    @inlinable
    public func succeed() {
        succeed(Void())
    }

}

[glbrntt]

Yes, something like that. Would you like to open a PR for this @mob-connection?