Fix case renames not marking previous casing as missing in time entries

[ijjk]

As noticed in vercel/next.js#10351 when a filename's casing is changed both variants of the filename are reported from getTimeInfoEntries. This makes users unable rely on getTimeInfoEntries as a safe source of truth on case insensitive file systems.

This PR attempts to correct this by when an event is triggered for a file that is already in the watcher's files it re-checks that the file is still present with exact casing by doing a readdir on the directory the file resides in.

The added test cases were tested and previously failing on:

• MacOS 10.14.6 (node: v12.14.1)
• Windows 10 Pro 1809 (node: v10.15.3)

I also tested against the added test case in vercel/next.js#10351 to double check this has the expected behavior.

[codecov]

Codecov Report

Merging #143 into master will decrease coverage by 0.14%.
The diff coverage is 100%.

@@            Coverage Diff            @@
##           master    #143      +/-   ##
=========================================
- Coverage   91.34%   91.2%   -0.15%     
=========================================
  Files           4       4              
  Lines         705     716      +11     
  Branches      185     188       +3     
=========================================
+ Hits          644     653       +9     
- Misses         61      63       +2

Impacted Files	Coverage Δ
lib/DirectoryWatcher.js	89.45% <100%> (-0.19%)	⬇️

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[sokra]

Thanks

[sokra]

If you want to you can also backport this to the watchpack-1 branch.

[ijjk]

Thanks for helping get this fix in! We're using watchpack@beta where this fix was specifically needed so if it's available there we should be good without backporting for now 🙏