Allow loading add-ons from multiple Node.js instances if they are
declared context-aware; in particular, this applies to N-API addons.

Also, plug a memory leak that occurred when registering N-API addons.

Refs: https://github.com/nodejs/node/pull/23319

PR-URL: https://github.com/nodejs/node/pull/26175
Fixes: https://github.com/nodejs/node/issues/21481
Fixes: https://github.com/nodejs/node/issues/21783
Fixes: https://github.com/nodejs/node/issues/25662
Fixes: https://github.com/nodejs/node/issues/20239
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>

Check whether calling into JS is allowed before doing so.

PR-URL: https://github.com/nodejs/node/pull/26127
Reviewed-By: Gus Caplan <me@gus.host>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>