domain: further abstract usage in C++

Move the majority of C++ domain-related code into JS land by introducing
a top level domain callback which handles entering & exiting the domain.

Move the rest of the domain necessities into their own file that creates
an internal binding, to avoid exposing domain-related code on the
process object.

Modify an existing test slightly to better test domain-related code.

PR-URL: https://github.com/nodejs/node/pull/18291


Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: James M Snell <jasnell@gmail.com>