feat: add mocha.mjs export

[brettz9]

PR Checklist

• Addresses an existing open issue: fixes 🚀 Feature: Ability to import mocha from ESM in the browser #5211
• That issue was marked as status: accepting prs
• Steps in CONTRIBUTING.md were taken

Overview

Adds an ESM export file for use in the browser.

The other non-underscored (private) keys I saw on the global mocha object which I wasn't sure which I might include were the following:

files, options, suite, isWorker, throwError, ui

[mark-wiemer]

For now let's exclude the private keys, they shouldn't be necessary for this export.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.69%. Comparing base (fb0215b) to head (a97ece6).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #5527   +/-   ##
=======================================
  Coverage   93.69%   93.69%           
=======================================
  Files          57       57           
  Lines        4390     4390           
  Branches      849      849           
=======================================
  Hits         4113     4113           
  Misses        277      277           

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[brettz9]

Thank you for the review!

I saw the linting failed after the merge, so I added my addition of /mocha.mjs to the eslint config file. There's also still a failure with /esm/mocha.js, a file that predated this PR, but with that file not being published, I wasn't sure what that was about. It technically is not even allowed with the ".js" extension since the package.json is type: 'commonjs'. Don't know if that file should be converted to .mjs, removed, treated as ESM by the linter anyways, or what?