fix(types): export InfiniteKeyedMutator

[LeoMcA]

https://github.com/vercel/swr/pull/2862/files added a new InfiniteKeyedMutator type, but didn't export it, which meant we had to use a rather roundabout fix:

// "swr/infinite" doesn't export InfiniteKeyedMutator directly
type InfiniteKeyedMutator<T> = SWRInfiniteResponse<
  T extends (infer I)[] ? I : T
>["mutate"];

It would be great if we could export this type directly, like KeyedMutator is.

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[agjs]

Can we merge this?

[eifr]

any updates regarding this one? im unable to upgrade atm as im using KeyedMutator as prop

[koba04]

I've changed the name to SWRInfiniteKeyedMutator for consistency