feat: Ability to get saved password options - getCredential

[Tkko]

Feature Request: Add Support for getCredential Method in Android Credential Manager

Objective:

Implement the getCredential method to enable users to access and select saved passwords from the Android Credential Manager, streamlining the sign-in process.

Tasks:

1. Investigate Android Credential Manager API:

   • Review the documentation for the getCredential method.

2. Create Platform-Specific Code:

   • Add a new method to SmartAuth for Android that calls getCredential.
   • Handle interactions with the native Android API using Pigeon.
   • Ensure seamless fallback behavior for unsupported Android versions.

3. Define Dart API:

   • Expose a clean Dart API for the feature in SmartAuth.
   • Example:

     Future<Credential?> getCredential();

4. Error Handling and Edge Cases:

   • Handle scenarios like user cancellation, or permission denial.
   • Return meaningful errors to the Flutter side when exceptions occur.

5. Documentation:

   • Update the package documentation to include:
     • Overview of the feature.
     • Example code for using getCredential.
     • Requirements for using the feature (e.g., API level).

6. Sample App Update:

   • Update the sample app in the package to demonstrate the usage of getCredential.