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.

Inizia individuando il metodo GetAvailablePublicKeyDevices() nella specifica e tutti i riferimenti a esso. Esamina la terminologia WebAuthn circostante, quindi stabilisci un nome sostitutivo non ambiguo e aggiorna il metodo in modo coerente; il lavoro sarà terminato quando l’API non utilizzerà più il termine fuorviante «dispositivi».

Scritto dal modello di indicizzazione a partire dal testo della issue.