Don't add file:// to windows path in CommonJS files. (mathjax/MathJax#3585)

[dpvc]

This PR fixes a problem with using MathJax CommonJS modules in node applications on windows. Apparently the file:// should not be added to absolute paths for CommonJS, but only should be for ESM modules.

Resolves issue mathjax/MathJax#3585.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.47%. Comparing base (907df71) to head (84ac9c8).

Additional details and impacted files

@@            Coverage Diff             @@
##           develop    #1519     +/-   ##
==========================================
  Coverage    86.47%   86.47%             
==========================================
  Files          340      340             
  Lines        86170    86176      +6     
  Branches      3210     4856   +1646     
==========================================
+ Hits         74513    74519      +6     
+ Misses       11657    11636     -21     
- Partials         0       21     +21     

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[zorkow]

I could not test. But lgtm.