Add topOrigin to clientData for cross-origin GET in iframe

[timcappalli]

This issue is to track the change discussed in the last WebAuthn call about adding the following for cross-origin GET in an frame:

• add top origin (topOrigin), aka what's shown to the user in the browser bar, to clientData (done in Allow for credential creation in a cross-origin iframe #1801)
• Add text around how RP should process and evaluate this information

This will match the changes being added in #1801 for create. PR coming in the next few weeks.

[Kieun]

In the latest editor's draft, topOrigin is missing in the get method's processing step 10.

Let collectedClientData be a new CollectedClientData instance whose fields are:
type
The string "webauthn.get".
challenge
The base64url encoding of pkOptions.challenge
origin
The serialization of callerOrigin.
crossOrigin
The inverse of the value of the sameOriginWithAncestors argument passed to this internal method.

[timcappalli]

Good catch @Kieun! TYVM. Addressed in #1891