Fix invalid type of credProps extension output

[geel9]

This PR resolves #415

• Adds new type, AuthenticationExtensionsCredentialPropertiesOutputs
  • This properly conforms to the output type defined in the spec.
• Changes AuthenticatorExtensionsClientOutputs.CredProps type from bool? to AuthenticationExtensionsCredentialPropertiesOutputs?
• Adds link to spec entry on credProps extension in XML comment for AuthenticatorExtensionsClientOutputs.CredProps to conform with comment pattern in rest of file

[abergs]

Hello @geel9 and thanks for the PR. I believe this is already solved in #411?

[geel9]

Hello @geel9 and thanks for the PR. I believe this is already solved in #411?

Ha -- so it is. I should've looked more carefully at the existing PRs.

[abergs]

I appreciate the effort to contribute!