Expose only public types from Auth exp

[Feiyang1]

1. Create a rollup d.ts file that only contains public types. Fixes alpha: Cannot find namespace 'gapi'. #4392
2. Remove unnecessary @internal annotations. @internal is only needed to hide members of public API, e.g. to hide internal methods of a public class. If something is not part of the API, there is no need to annotate it.

[changeset-bot]

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Latest commit: 36219c9

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