chore: Export fetchAuthSession input & output types

[jimblanc]

Description of changes

Export the fetchAuthSession input & output types from aws-amplify/auth, in line with our other v6 APIs.

Issue #, if available

Description of how you validated changes

Local testing

Checklist

• PR description included
• yarn test passes
• Tests are changed or added
• Relevant documentation is changed or added (and PR referenced)

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[jimblanc]

Made the return type here more explicit

[ashika112]

Can we confirm is there is a test for this use case also probably type those too? What are your thoughts?

[jxdp]

The Amplify Auth package has come a long way with the V6 upgrade, it's great to see.

For the sake of consistency, perhaps this PR should also add a FetchAuthSessionOutput = AuthSession alias so that it is consistent with the other methods, such as

• getCurrentUser with GetCurrentUserOutput (= AuthUser)
• fetchUserAttributes with FetchUserAttributesOutput (= AuthUserAttributes<UserAttributeKey>)

Perhaps AuthUserAttributes could also be exported (since UseAttributeKeys already is).