Find a better name for "devices" in GetAvailablePublicKeyDevices

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From the documentation:
> The word "devices" is used broadly and can refer to individual authenticators (like a locked passkey provider or linked hybrid device), a group of authenticators on a transport (USB or hybrid QR code devices), or even an individual credential (in the case of credentials supplied by unlocked passkey providers).

We should choose a different word besides "devices" that isn't so confusing. "sources" probably works better. It was originally avoided because there is a term for _credential sources_ in the WebAuthn spec that means something else, but perhaps it wouldn't be confusing in this case.

I'm open to other alternatives too.

This would change the name of the `GetAvailablePublicKeyDevices()` method.

Beginne damit, die Methode GetAvailablePublicKeyDevices() in der Spezifikation und alle Verweise darauf zu finden. Überprüfe die umgebende WebAuthn-Terminologie, lege dann einen eindeutigen Ersatznamen fest und aktualisiere die Methode einheitlich; fertig ist die Aufgabe, wenn die API den verwirrenden Begriff „Geräte“ nicht mehr verwendet.

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