src: move default assignment of async_id_ in async_wrap.h

Moving the default assignment of async_id from the constructor in
async_wrap.cc to class definition in async_wrap.h

PR-URL: https://github.com/nodejs/node/pull/23495


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Shelley Vohr <codebytere@gmail.com>
Reviewed-By: Sakthipriyan Vairamani <thechargingvolcano@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>