Demo: Use PublicKeyCredential parse functions instead of converting by hand

[Edduaardo]

Use PublicKeyCredential functions parseCreationOptionsFromJSON(), parseRequestOptionsFromJSON() and toJSON() to convert between Base64Url and ArrayBuffers instead of doing it by hand, as it is the recommended way now. It also stops using the deprecated extensions property in favor of clientExtensionResults.

https://developer.mozilla.org/en-US/docs/Web/API/PublicKeyCredential/parseCreationOptionsFromJSON_static
https://developer.mozilla.org/en-US/docs/Web/API/PublicKeyCredential/parseRequestOptionsFromJSON_static
https://developer.mozilla.org/en-US/docs/Web/API/PublicKeyCredential/toJSON

[Edduaardo]

@dotnet-policy-service agree

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 78.62%. Comparing base (40b302c) to head (8784f4c).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #654   +/-   ##
=======================================
  Coverage   78.62%   78.62%           
=======================================
  Files          98       98           
  Lines        2545     2545           
  Branches      423      423           
=======================================
  Hits         2001     2001           
  Misses        434      434           
  Partials      110      110           

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[abergs]

Thank you for the contribution @Edduaardo!