[FR]: Complete macOS Support for Firebase Auth

### Description

# Feature Request: Complete macOS Support for Firebase Auth

## Problem Statement
Currently, Firebase Auth has limited support for macOS platforms, which prevents developers from creating cross-platform applications that require authentication on macOS. While some basic functionality exists, full feature parity with iOS is needed.

## Proposed Solution
Extend the Firebase Auth SDK to provide complete macOS support, matching the functionality available on iOS. This would include:
- Full authentication provider support (Email/Password, Google Sign-In, Apple Sign-In, etc.)
- Proper handling of macOS-specific authentication flows
- Support for both Catalyst and native macOS apps
- Comprehensive documentation for macOS implementation

## Technical Details
- Target Platform: macOS (both Catalyst and native)
- Current Status: Partial support exists but lacks complete feature parity
- Dependencies: Firebase iOS SDK

## Use Case
As a developer building cross-platform applications, I need to implement Firebase Auth on macOS to:
- Provide consistent authentication experience across iOS, Android, and macOS
- Enable desktop applications to use Firebase authentication
- Support modern authentication methods on macOS platforms

## Additional Context
- This would complement the existing iOS SDK
- Would enable better cross-platform development workflows
- Aligns with the growing trend of desktop applications using web technologies

## Contribution
I am willing to contribute to this effort and can help with:
- Testing on macOS platforms
- Providing feedback on implementation
- Contributing to documentation

## Related Issues
- Current partial support documented at: https://firebase.google.com/docs/ios/learn-more
- Related to React Native Firebase issue: #8572 - https://github.com/invertase/react-native-firebase/issues/8572

### API Proposal

_No response_

### Firebase Product(s)

Authentication