src: make AsyncWrap constructors delegate

Currently, there is an AsyncWrap constructor that is only used by
PromiseWrap. This constructor has a body which is very similar
to the other AsyncWrap constructor.

This commit suggests updating the private constructor that is used
by PromiseWrap and also have the second constructor delegate to this
one to avoid the code duplication.

PR-URL: https://github.com/nodejs/node/pull/19366


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Minwoo Jung <minwoo@nodesource.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>