feat: generate paragon-theme.json during npm run build with themeUrls

[adamstankiewicz]

Description

Generates a paragon-theme.json file in dist output directory containing relative paths to the compiled core and theme variant CSS paths:

{
  "themeUrls": {
    "core": {
      "default": "./core.css",
      "minified": "./core.min.css"
    },
    "variants": {
      "light": {
        "default": "./light.css",
        "minified": "./light.min.css"
      }
    }
  }
}

The paragon.config.json file will be parsed by @edx/frontend-build to avoid needing to hardcode core.min.css or light.min.css into its code explicitly, rather relying on the paths provided by Paragon itself.

Related PR: openedx/frontend-build#365

Deploy Preview

N/A

Merge Checklist

• If your update includes visual changes, have they been reviewed by a designer? Send them a link to the Netlify deploy preview, if applicable.
• Does your change adhere to the documented style conventions?
• Do any prop types have missing descriptions in the Props API tables in the documentation site (check deploy preview)?
• Were your changes tested using all available themes (see theme switcher in the header of the deploy preview, under the "Settings" icon)?
• Were your changes tested in the example app?
• Is there adequate test coverage for your changes?
• Consider whether this change needs to reviewed/QA'ed for accessibility (a11y). If so, please add wittjeff and adamstankiewicz as reviewers on this PR.

Post-merge Checklist

• Verify your changes were released to NPM at the expected version.
• If you'd like, share your contribution in #show-and-tell.
• 🎉 🙌 Celebrate! Thanks for your contribution.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.02%. Comparing base (9a94ac5) to head (20b90b6).
Report is 908 commits behind head on alpha.

Additional details and impacted files

@@           Coverage Diff           @@
##            alpha    #2333   +/-   ##
=======================================
  Coverage   91.02%   91.02%           
=======================================
  Files         214      214           
  Lines        3534     3534           
  Branches      860      860           
=======================================
  Hits         3217     3217           
  Misses        309      309           
  Partials        8        8           

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[brobro10000]

Approved with a minor nit of renaming some of the variables from ParagonConfig to ParagonThemingConfig but no big deal 👍🏽

[edx-semantic-release]

🎉 This PR is included in version 21.0.0-alpha.29 🎉

The release is available on:

• npm package (@alpha dist-tag)
• GitHub release

Your semantic-release bot 📦🚀

[edx-semantic-release]

🎉 This PR is included in version 22.0.0-alpha.1 🎉

The release is available on:

• npm package (@alpha dist-tag)
• GitHub release

Your semantic-release bot 📦🚀

[openedx-semantic-release-bot]

🎉 This PR is included in version 23.0.0-alpha.1 🎉

The release is available on:

• npm package (@alpha dist-tag)
• GitHub release

Your semantic-release bot 📦🚀

[openedx-semantic-release-bot]

🎉 This PR is included in version 23.0.0 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

Your semantic-release bot 📦🚀