[google_sign_in] Redesign API for current identity SDKs - Platform Implementations

[stuartmorgan-g]

This is the platform implementation portion of #9267

Part of flutter/flutter#119300

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[stuartmorgan-g]

This is #9267 with the following changes:

• platform interface changes removed
• platform interface dependencies changed to the newly-published 3.0 instead
• app-facing package changes removed
• implementation packages added to the temporary build-all exclusion to prevent conflicts there.

[bparrishMines]

LGTM

[auto-submit]

autosubmit label was removed for flutter/packages/9479, because - The status or check suite Linux repo_checks has failed. Please fix the issues identified (or deflake) before re-applying this label.