Fix Turbopack resolution through chained symlinks (#97825)
## Summary
- classify symlinks by the final target of the full chain with
`LinkTarget::resolved_type`
- preserve non-directory behavior for dangling, invalid, and cyclic
chains and retain the existing ancestor-loop guard
- fold two-hop directory-symlink coverage into the existing production
symbolic-links suite
Fixes #97786.
## Verification
- `CARGO_INCREMENTAL=0 pnpm build-all`
- `cargo test -p turbo-tasks-fs
test_link_target_resolved_type_through_chain -- --nocapture`
- `cargo test -p turbo-tasks-fs read_glob_symlinks -- --nocapture`
- `cargo test -p turbopack-core test_read_matches -- --nocapture`
- `cargo clippy -p turbo-tasks-fs -p turbopack-core --all-targets -- -D
warnings`
- `cargo fmt --all -- --check`
- `pnpm test-start-turbo test/production/app-dir/symbolic-links -t
"chained directory symlinks"`
- manually verified `/directory-symlink-chain` under `next dev
--turbopack`
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Co-authored-by: Benjamin Woodruff <benjamin.woodruff@vercel.com>
