Consider less generic term for the `Availability` enum?

[tidoust]

The term Availability is fairly generic but means something specific to the context of this API. It may be worth considering a more specific name for the enumeration, e.g. with a prefix as in SummarizerAvailability, or more explicit about the meaning as in LocalAvailability or LocalDeviceAvailability.

[domenic]

I'd be happy to rename this if we ever came into a conflict. But enum names are completely unobservable so we can do this at any time, including in the event of such a future conflict.`