fix: rename box-shadow-control SCSS mixin to pgn-box-shadow

[adamstankiewicz]

Description

This is a new SCSS mixin, which gives consumers the ability to add elevation (i.e., elevation) based on the pre-defined elevation levels in addition to a direction/side (e.g., top, right, centered).

Deploy Preview

n/a (SCSS change only. There probably should be an Elevation foundations page in the documentation website. Taking an action item to file this ticket).

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)?
• 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.

[netlify]

✅ Deploy Preview for paragon-openedx ready!

Name	Link
🔨 Latest commit	b870df2
🔍 Latest deploy log	https://app.netlify.com/sites/paragon-openedx/deploys/624306c1d7713a000a4fce0c
😎 Deploy Preview	https://deploy-preview-1195--paragon-openedx.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify site settings.

[codecov]

Codecov Report

Merging #1195 (b870df2) into master (432f47d) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1195   +/-   ##
=======================================
  Coverage   90.74%   90.74%           
=======================================
  Files         193      193           
  Lines        3067     3067           
  Branches      691      691           
=======================================
  Hits         2783     2783           
  Misses        271      271           
  Partials       13       13           

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 432f47d...b870df2. Read the comment docs.

[edx-semantic-release]

🎉 This PR is included in version 19.13.3 🎉

The release is available on:

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

Your semantic-release bot 📦🚀