fix(typescript-estree): normalize paths to fix cache miss on windows

[bradzacher]

Fixes #1126

Windows paths can come in with forward or back slashes.
Need to normalize the paths so they have the same slashes.

NGL switching from mac to windows to do this was so painful.

[typescript-eslint]

Thanks for the PR, @bradzacher!

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[platinumazure]

Curious how this could be tested...

[bradzacher]

We've got great coverage of Mac (because that's what I dev on), and linux (because that's what the CI currently runs on), but no coverage on windows.

That didn't matter in the past, because we never did anything around filenames.
With the addition of this "watching" code, we need to add windows integration tests to the CI.

@JamesHenry said that it's easy to setup on our CI, but I don't know how to configure it 😅

[codecov]

Codecov Report

Merging #1128 into master will increase coverage by <.01%.
The diff coverage is 33.33%.

@@            Coverage Diff             @@
##           master    #1128      +/-   ##
==========================================
+ Coverage   94.07%   94.07%   +<.01%     
==========================================
  Files         120      120              
  Lines        5213     5214       +1     
  Branches     1443     1443              
==========================================
+ Hits         4904     4905       +1     
  Misses        177      177              
  Partials      132      132

Impacted Files	Coverage Δ
...ges/typescript-estree/src/create-program/shared.ts	80% <33.33%> (+1.42%)	⬆️