refactor(Checkbox): use characters for check state

[booc0mtaco]

Test Plan:

• Update snapshots
• Wrote automated tests
• CI tests / new tests are not applicable
• Manually tested my changes, but I want to keep the details secret
• Created and used an alpha publish
• Manually tested my changes, and here are the details:

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.78%. Comparing base (24815c2) to head (e065400).

Additional details and impacted files

@@                 Coverage Diff                 @@
##           v15-components-2.0    #1966   +/-   ##
===================================================
  Coverage               96.78%   96.78%           
===================================================
  Files                     141      141           
  Lines                    3572     3572           
  Branches                  972      972           
===================================================
  Hits                     3457     3457           
  Misses                    112      112           
  Partials                    3        3           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.