src: make process.dlopen() load well-known symbol

Look for symbol `node_register_module_v${NODE_MODULE_VERSION}` if the
add-on didn't self-register.  This can be used to create add-ons that
support multiple Node.js versions from a single shared object.

PR-URL: https://github.com/nodejs/node/pull/18934


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Daniel Bevenius <daniel.bevenius@gmail.com>
Reviewed-By: Franziska Hinkelmann <franziska.hinkelmann@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: Matheus Marchini <matheus@sthima.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>