feat(fs/unstable): add readDir

[jbronder]

This PR adds the readDir API to @std/fs, which is a function intended to mirror Deno.readDir.

Towards #6255.

[codecov]

Codecov Report

Attention: Patch coverage is 37.93103% with 18 lines in your changes missing coverage. Please review.

Project coverage is 96.40%. Comparing base (3c1b8e9) to head (aa613c9).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
fs/unstable_read_dir.ts	50.00%	10 Missing ⚠️
fs/_to_dir_entry.ts	11.11%	8 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6338      +/-   ##
==========================================
- Coverage   96.44%   96.40%   -0.04%     
==========================================
  Files         547      549       +2     
  Lines       41812    41841      +29     
  Branches     6348     6350       +2     
==========================================
+ Hits        40325    40337      +12     
- Misses       1447     1464      +17     
  Partials       40       40              

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[kt3k]

LGTM. Thank you!