fs: prevent spurious recursive watch events on prefix siblings

[marcopiraccini]

Fix a bug in the JS-based recursive fs.watch (used on Linux) where deleting an entry caused spurious rename events to be emitted for unrelated sibling entries whose names share a prefix with the deleted entry.

FSWatcher#unwatchFiles(file) in lib/internal/fs/recursive_watch.js used StringPrototypeStartsWith(filename, file) to find the watched entries to remove. This match is a raw string prefix, so deleting foo also unwatched foo_, foo_bar, foo_bar/file.txt, and so on. The next time #watchFolder walked the parent directory, those still-on-disk siblings were missing from #files and were treated as newly created, firing extra rename events and re-attaching watchers redundantly.

Fix

Match by exact path, or by deletedPath + path.sep prefix, so only the deleted entry and its actual descendants are unwatched.

Fixes: #58868

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.66%. Comparing base (b2f6aa3) to head (7b92f84).

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #63095      +/-   ##
==========================================
+ Coverage   89.65%   89.66%   +0.01%     
==========================================
  Files         712      712              
  Lines      220512   220515       +3     
  Branches    42289    42282       -7     
==========================================
+ Hits       197690   197718      +28     
+ Misses      14663    14652      -11     
+ Partials     8159     8145      -14     

Files with missing lines	Coverage Δ
lib/internal/fs/recursive_watch.js	87.11% <100.00%> (+1.84%)	⬆️

... and 22 files with indirect coverage changes

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