chore: update example app on how to embed SwiftUI auth in UIKit

[russellwheatley]

• Updated example app to demonstrate how to embed FirebaseUI Swift into UIKit app.

[gemini-code-assist]

Summary of Changes

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This pull request introduces a valuable example to the sample application, illustrating how to effectively integrate SwiftUI-based Firebase authentication flows into existing UIKit view hierarchies. This enhancement provides developers with a flexible approach to leverage modern SwiftUI authentication components while maintaining their established UIKit application structure, facilitating a smoother transition and adoption of new frameworks.

Highlights

• New Example Added: A new example demonstrating how to embed FirebaseSwiftUI authentication within a UIKit application has been added.
• UIKit Integration: The example utilizes UIViewControllerRepresentable to host a SwiftUI AuthPickerView inside a UIKit UIViewController, showcasing seamless integration.
• Authentication Flow Demonstration: The new example includes UI elements and logic to clearly illustrate both unauthenticated and authenticated states within the embedded view.

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[gemini-code-assist]

Code Review

This pull request adds a helpful example demonstrating how to embed Firebase's SwiftUI authentication views within a UIKit application. The implementation is generally well-structured, using UIViewControllerRepresentable to bridge between SwiftUI and UIKit. I've identified a couple of areas for improvement to enhance the clarity and correctness of the example code. Specifically, I've suggested simplifying the makeUIViewController method and refining the logic for presenting the authentication sheet to provide a more intuitive user experience. Overall, this is a valuable addition to the sample app.

[gemini-code-assist]

The call to viewController.update(authService: authService) is redundant because updateUIViewController(_:context:) is called by the system immediately after makeUIViewController(context:). All view controller configuration and data passing from SwiftUI should be done in updateUIViewController for clarity and to follow best practices. This also avoids performing the update work twice.

  func makeUIViewController(context: Context) -> EmbeddedAuthViewController {
    return EmbeddedAuthViewController()
  }

[gemini-code-assist]

This onChange modifier automatically presents the authentication sheet whenever the user is not authenticated. This behavior can be confusing for a user, as the sheet will appear immediately upon signing out, and it makes the "Authenticate" button in your UI redundant. For an example demonstrating an embedded view, it would be clearer to allow the user to manually trigger the authentication flow via the button. I recommend removing this automatic presentation logic.