src: prefer to get `Environment` from `Context`

We explicitly store the context anyway, and can skip the
extra steps introduced in `Environment::GetCurrent()`.

PR-URL: https://github.com/nodejs/node/pull/26376


Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>