turbopack: Implement Server Actions from Client Components (#57391)
### What?
This completes Turbopack's Server Actions implementation!
It also cleans up several things:
- Removes `server_actions` configuration, it's enabled by default now.
- Fixes the transform that runs in the SSR layer (it actually needs to
use the client transform)
- Generates a new encryption key
### Why?
### How?
It crawls the client layer modules for additional Server Actions
imports, and adds them to our generated `actions.js` entry point.
Closes NEXT-
Fixes #
Closes WEB-1854
---------
Co-authored-by: kodiakhq[bot] <49736102+kodiakhq[bot]@users.noreply.github.com>