src: unload addons when environment quits

This is an alternative to https://github.com/nodejs/node/pull/23319
which attaches the loaded addons to the environment and closes them
when the environment is destroyed.

PR-URL: https://github.com/nodejs/node/pull/24861


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>