Add AAGUID to credProps

[timcappalli]

In the TPAC discussions, there was a desire to rely solely on AAGUID for passkey provider / authenticator naming, and to remove authenticatorDisplayName from credProps.

The challenge is that authenticatorDisplayName is available on .get and the AAGUID is not. AAGUID on .get allows an RP to update the user visible name if a passkey is migrated between providers.

Proposed Change

Potential options:

1. Add a client extension for AAGUID on .get
2. Add AAGUID to credProps
3. Keep authenticatorDisplayName instead
4. Adding back attestation on get

I think option 2 was the preferred path from the discussion?