[webauthn] Is AuthenticationExtensionsAuthenticatorInputs unused? (#1435)

emlun has just created a new issue for https://github.com/w3c/webauthn:

== Is AuthenticationExtensionsAuthenticatorInputs unused? ==
[§5.7.3](https://w3c.github.io/webauthn/#iface-authentication-extensions-authenticator-inputs) lists the definition:

```
typedef record<DOMString, DOMString> AuthenticationExtensionsAuthenticatorInputs;
```

...which seems to not be referenced anywhere else in the spec, extensions certainly use output types other than `DOMString`. Is this type unused?

While working on #1425 I started thinking about adding a simlar CDDL extension point. Should we perhaps transmute it into CDDL (as WebIDL doesn't seem entirely appropriate for the authenticator layer) and update it to match the extensions?

Please view or discuss this issue at https://github.com/w3c/webauthn/issues/1435 using your GitHub account