WebAuthn API error messages too vague when Touch ID is unavailable

• Component: WebKit Misc.
• Status: NEW ---

Created attachment 427429 [details]
Screenshot of console error output from call to `navigator.credentials.create()`

It appears that Safari 14.1 (on macOS 11.3) no longer supports access to Touch ID when a MacBook is in clamshell mode. Attempts to call `navigator.credentials.create()` while specifying "platform" in authenticator selection fail with the following console message:

> Unhandled Promise Rejection: NotAllowedError: This request has been cancelled by the user.
The confusion comes from the fact that the user is never shown any UI to interact with; the request immediately errors out with no clue except for this single error message! It was only after some frantic testing that I discovered it was because the laptop was closed. When I opened the laptop then the same code worked as expected, with Safari prompting me to interact with Touch ID.

For sake of example here's what I'm passing in within attestation options to try and access Touch ID:

```
"authenticatorSelection": {
  "authenticatorAttachment": "platform",
  "requireResidentKey": false,
  "userVerification": "required"
}
```

Is it possible to clarify this error message to indicate that the request is erroring out because Touch ID is unavailable (for whatever reason)? It'll make it easier to debug this issue in the future as it'll be more obvious why seemingly functional code "stopped working for some reason".

[Radar WebKit Bug Importer]

<rdar://problem/77658896>