Avoid obsolete pnpm overrides in pack-next (#99199)
### What?
Make `pack-next` choose pnpm override locations from the destination
workspace root's pinned `packageManager` version.
### Why?
pnpm 11+ warns about `pnpm.overrides` in `package.json` and ignores that
setting. Conversely, rewriting `pnpm-workspace.yaml` for older pnpm
versions creates unnecessary churn.
### How?
Use the repository's `semver` package to read the major from a pinned
pnpm version. For a pnpm 11+ destination, merge overrides into the
existing/detected pnpm workspace file without adding `pnpm.overrides` to
`package.json`. For pnpm 10 and older, update only the package.json
field. When the pin is missing or unusable, retain the previous
dual-write behavior. Existing user overrides and npm/Yarn override
behavior are preserved.
### Verification
- Passed eleven temporary destination scenarios covering pinned
older/newer pnpm, existing overrides and workspace files, nested
workspace roots, and unknown versions.
- Prettier check, Node syntax check, and `git diff --check` passed.
- Repo-wide lint/typecheck not run (root dependencies are not installed
in this checkout).
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Co-authored-by: vercel-fleet-prod[bot] <318278635+vercel-fleet-prod[bot]@users.noreply.github.com>
Co-authored-by: Will Binns-Smith <755844+wbinnssmith@users.noreply.github.com>
