feat: deprecate core's Node.js module

[louis-menlo]

Problem
All of the extensions are now CommonJS modules. We don't need to expose the core here, since there is now only one shared backend.

There is no need to proxy the Filesystem, Networking, or Processing for browser extension use; you can import them directly from Backend Extensions.

Success Criteria
A clear and concise description of what you want to happen.

Additional context
Add any other context or screenshots about the feature request here.

[louis-menlo]

It's deprecated. Since we moved extensions to BE