src: avoid Isolate::GetCurrent() for platform implementation

There’s no need to use `Isolate::GetCurrent()`, which is generally
discouraged, as the `Isolate*` pointer can generally be looked up
from the per-Isolate platform data structure.

PR-URL: https://github.com/nodejs/node/pull/32269


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Gus Caplan <me@gus.host>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: James M Snell <jasnell@gmail.com>