async_hooks: set unhandledRejection async context

This commit now executes `process.on('unhandledRejection')` in the
async execution context of the concerned `Promise`.

PR-URL: https://github.com/nodejs/node/pull/37281


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>