Electron mocha renderer migration

[araujoarthur0]

Related issue

Helps #1037

Context / Background

Continues from #1061

This one is adding the renderer version of the mocha run.
It has to be in a separate npm script because the --renderer switch has to be passed to electron-mocha.

Also, mocha needed a patch because it was getting stuck while opening the tests.

I used themes.js as a sample. I added the sinon package which allows us to add stub functions with call counts, something we used to rely on jest to have. Then I replaced the jquery in the test with stubbed functions since we are not really testing the jquery effects.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 57.85%. Comparing base (3a4e99f) to head (be788cd).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1065   +/-   ##
=======================================
  Coverage   57.85%   57.85%           
=======================================
  Files          22       22           
  Lines        3270     3270           
  Branches      425      425           
=======================================
  Hits         1892     1892           
  Misses       1378     1378           

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[tupaschoal]

Not sure I understood it fully, but seems pretty organized. Having the call count seems nice!