docs(auth): add Credential Manager Google Sign-In support and safety guards

[rutvik24]

Description

This PR updates the Authentication documentation to incorporate support for Google Sign-In using the new Credential Manager API via the react-native-nitro-google-sign-in package. It also introduces safety improvements and link corrections in the social authentication guides.

Key Changes:

• Credential Manager Support: Added comprehensive documentation and code examples for implementing Google Sign-In using react-native-nitro-google-sign-in.
• Safety Improvements: Updated existing Google Auth examples to include a safety check for auth().currentUser before calling linkWithCredential, preventing potential runtime errors.
• Link Corrections: Fixed documentation links for the react-native-nitro-google-sign-in library to ensure they point to the correct resources.

Checklist

• I have read the CONTRIBUTING.md guide.
• I have updated the documentation accordingly.
• My changes follow the existing style and conventions of the project.

[gemini-code-assist]

Summary of Changes

Hello, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request enhances the Authentication documentation by introducing support for the Credential Manager API via the react-native-nitro-google-signin package. It also improves the robustness of existing social authentication guides by adding necessary safety checks and clarifying library-specific implementation details.

Highlights

• Credential Manager Support: Added comprehensive documentation and code examples for implementing Google Sign-In using the react-native-nitro-google-signin library.
• Safety Improvements: Updated social authentication examples to include null checks for auth().currentUser before calling linkWithCredential to prevent runtime errors.
• Documentation Updates: Corrected documentation links and clarified the usage of revokeAccess across different Google sign-in libraries.

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[gemini-code-assist]

Code Review

This pull request updates the Google social authentication documentation to introduce react-native-nitro-google-signin as a free alternative supporting Android's Credential Manager, comparing it with @react-native-google-signin/google-signin and providing updated code examples for both. The review feedback highlights potential runtime TypeError risks in the code snippets due to missing optional chaining on response.data, as well as several typos in the documentation URLs for both libraries.

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[gemini-code-assist]

There is a typo in the documentation URL for @react-native-google-signin/google-signin. It should be react-native-google-signin.github.io instead of react-native-google-sign-in.github.io.

[mikehardy]

looks great. gemini missed on one in the review but the possibility of response.data being undefined seems legit and it's easy enough to do optional chaining. I've proposed two suggestions there which I'll be able to commit via github web UI once I finish the review. So I'll approve the PR, commit the suggestions, then squash-merge this in

Thanks!