fs: preserve filename when recursive watch root file is removed

[cuishuang]

When the JavaScript recursive watcher is used, removing a watched root file emits an empty filename.

This happens because the deletion path uses the root-relative filename, and the relative path of the root file to itself is empty. The same watcher emits the basename for change events, while native recursive watchers also report the basename.

Emit the basename in the root-file deletion branch to keep the result consistent with change events and native recursive watchers.

Tests:

• Add a regression test for fsPromises.watch() on a root file.
• Update the existing Linux recursive watcher expectation.

Refs: #65486

[github-actions]

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.18%. Comparing base (9f7ae86) to head (f2f3382).
⚠️ Report is 7 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #65882      +/-   ##
==========================================
- Coverage   90.19%   90.18%   -0.01%     
==========================================
  Files         771      771              
  Lines      264911   265094     +183     
  Branches    50323    50351      +28     
==========================================
+ Hits       238939   239082     +143     
- Misses      16922    16963      +41     
+ Partials     9050     9049       -1     

Files with missing lines	Coverage Δ
lib/internal/fs/recursive_watch.js	85.12% <100.00%> (ø)

... and 38 files with indirect coverage changes

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