fix(fs): improve the docs and error message of ensureSymlink(Sync)

[kt3k]

This PR addresses the feedback given in #6191

This PR improves the error message of fs.ensureSymlink when the link target doesn't exist. Also this improves the documentation by adding examples.

closes #6191

[codecov]

Codecov Report

Attention: Patch coverage is 80.00000% with 4 lines in your changes missing coverage. Please review.

Project coverage is 96.57%. Comparing base (82ccee6) to head (9361eb0).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
fs/ensure_symlink.ts	80.00%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6198      +/-   ##
==========================================
- Coverage   96.58%   96.57%   -0.02%     
==========================================
  Files         532      532              
  Lines       40801    40819      +18     
  Branches     6105     6111       +6     
==========================================
+ Hits        39409    39422      +13     
- Misses       1350     1355       +5     
  Partials       42       42              

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[satyarohith]

LGTM

Nit: update target param description that it should be relative to dirname of linkName when it's a string?

[kt3k]

Nit: update target param description that it should be relative to dirname of linkName when it's a string?

Sounds good! Updated