Consider exposing claims for username, email, phone etc in id_token in a more user friendly way

Currently there is no way to obtain username/email/phone after obtaining the refresh token. User info also doesn't expose these information (there is only `isAnonymous`, `isVerified` and `sub` now). Consider adding these info in userinfo, or implementing extracting username/email/phone in `id_token`'s claims.

Things to consider:
- Username/email/phone might each be optional
- Additional data bundled together with each authenticator (e.g. phone might come with 852? Just an example)

Start by tracing how the Android SDK obtains and exposes the refresh token, userinfo, and id_token claims. Clarify whether the intended API is userinfo, id_token extraction, or both, then define handling for optional username, email, phone, and authenticator-specific data before implementation.

Written by the indexing model from the issue text.