src: move worker_context from Environment to IsolateData

Workers are fully in control of their Isolates, and this helps
avoid a problem with later changes to `CreateEnvironment()`
because now we can run the boostrapping code inside the latter.

PR-URL: https://github.com/nodejs/node/pull/30467


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>