Prepare `'use cache'` for static root-param tracking (#99239)
Static root-param tracking for `'use cache'` needs to distinguish which
getters a cached module imports. The existing generated module contains
every getter, so module-level dependency collection includes unrelated
root params.
`next/root-params` now re-exports each getter from a separate virtual
module. The generated `next/root-params` module declares that it has no
side effects, so Turbopack resolves named imports without including
unrelated getter modules. Runtime root-param tracking remains unchanged.
The split also keeps code hashes stable when unrelated root params are
added. The regression test checks this dependency isolation through the
existing code-hash manifest.
