fs: honor dereference for symlinks nested in cpSync trees

[christianaurichzm]

fs.cpSync(src, dest, { dereference: true, recursive: true }) copies symlinks found inside the tree as symlinks. Reported in #59168 as a regression in 22.17, and still present on main:

$ mkdir src linked && touch linked/foo && ln -s ../linked/foo src/bar
$ node -e "fs.cpSync('./src', './out', { dereference: true, recursive: true })"
$ ls -l out
lrwxrwxrwx bar -> /tmp/.../linked/foo

Cause

When no filter is given, cp-sync.js hands the whole tree to fsBinding.cpSyncCopyDir(). That C++ loop recreates every symlink it finds and consults dereference only for the subdirectory-of-self guards, so it never copies the target.

A symlink passed as src is unaffected because getStats() resolves that one with statSync() before the native copy starts. This is why the existing dereference tests pass and why the option only fails for links inside the tree.

Fix

With dereference enabled, links resolving to directories or regular files use the corresponding native copy paths, which already follow symlinks. Dangling links have no target to copy and are reported instead.

Existing destinations follow the JavaScript walker's force and errorOnExist behavior, including file/directory conflicts.

Verification

The new test fails on main and passes with the patch. I also compared the destination cases against the JavaScript path by passing a filter, which keeps the copy out of the native walker.

On Linux x64:

• make lint
• parallel
• sequential
• es-module

all pass.

#65488 refactors the same native walker. If it lands first, I can rebase this fix onto the new implementation.

Fixes: #59168

[codecov]

Codecov Report

❌ Patch coverage is 72.54902% with 14 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.05%. Comparing base (e06b0f1) to head (346ed1c).
⚠️ Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
src/node_file.cc	72.54%	8 Missing and 6 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #65731      +/-   ##
==========================================
- Coverage   90.06%   90.05%   -0.02%     
==========================================
  Files         754      754              
  Lines      256388   256439      +51     
  Branches    48494    48517      +23     
==========================================
- Hits       230926   230925       -1     
- Misses      16574    16611      +37     
- Partials     8888     8903      +15     

Files with missing lines	Coverage Δ
src/node_file.cc	74.17% <72.54%> (-0.02%)	⬇️

... and 36 files with indirect coverage changes

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