Show loader for disabled checkbox for download-as-default landing page - WT127 (fix #433)

[wen-2018]

One-line summary

This PR adds a loader for temporarily disabled checkbox for Windows landing page download-as-default option.

Significant changes and points to review

Firefox on Windows landing page download-as-default checkbox.

Issue / Bugzilla link

https://mozilla-hub.atlassian.net/browse/WT-127?atlOrigin=eyJpIjoiMjgyY2E5YThjOWU2NGRmMWI1MzliMjE4YmYwYzY0ODgiLCJwIjoiaiJ9
#433

Testing

http://localhost:8000/en-US Firefox on Windows

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 77.81%. Comparing base (2f685c4) to head (41ca15f).
⚠️ Report is 54 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #905   +/-   ##
=======================================
  Coverage   77.81%   77.81%           
=======================================
  Files         131      131           
  Lines        8091     8091           
=======================================
  Hits         6296     6296           
  Misses       1795     1795           

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[maureenlholland]

requested change: spinner animation with no layout shift

suggested changes are non-blocking

[maureenlholland]

@wen-2018 I'm inclined to close this as outdated. We've turned off the download-as-default checkbox for now and the home page has moved to CMS.

It might be worth moving to a more systematized feature related to Flare26. We might want to formalize some standard UI loading options in context of buttons and checkboxes

[wen-2018]

Closed as it is outdated.