feat: add API methods for providing received extension information

[santiagorodriguez96]

What

Add the possibility of accessing to the client and authenticator extensions outputs in the PublicKeyCredential's models, so that it can be manually validated by the user according to their expectations.

Why

Extracted from WebAuthn spec in the sections 7.1 Registering a New Credential (step 17) and 7.2 Verifying an Authentication Assertion (step 18):

Verify that the values of the client extension outputs in clientExtensionResults and the authenticator extension outputs in the extensions in authData are as expected, considering the client extension input values that were given in options.extensions and any specific policy of the Relying Party regarding unsolicited extensions, i.e., those that were not specified as part of options.extensions. In the general case, the meaning of "are as expected" is specific to the Relying Party and which extensions are in use.

Note: Client platforms MAY enact local policy that sets additional authenticator extensions or client extensions and thus cause values to appear in the authenticator extension outputs or client extension outputs that were not originally specified as part of options.extensions. Relying Parties MUST be prepared to handle such situations, whether it be to ignore the unsolicited extensions or reject the attestation. The Relying Party can make this decision based on local policy and the extensions in use.

Note: Since all extensions are OPTIONAL for both the client and the authenticator, the Relying Party MUST also be prepared to handle cases where none or not all of the requested extensions were acted upon.

[santiagorodriguez96]

The above was an accidental delete of this thread. Sorry about that.