feat(auth)!: remove deprecated functions

[Lyokone]

This PR removes all deprecated methods from the firebase_auth package in preparation for a breaking change release.

Removed Methods

• ActionCodeSettings.dynamicLinkDomain - Firebase Dynamic Links is deprecated and will be shut down
• MicrosoftAuthProvider.credential() - Use signInWithProvider(MicrosoftAuthProvider) instead
• FirebaseAuth.instanceFor() persistence parameter - Use setPersistence() instead
• FirebaseAuth.fetchSignInMethodsForEmail() - Removed for security best practices
• User.updateEmail() - Use verifyBeforeUpdateEmail() instead

Migration Guide

ActionCodeSettings

// Before
ActionCodeSettings(
  url: 'https://example.com',
  dynamicLinkDomain: 'example.page.link',
)

// After
ActionCodeSettings(
  url: 'https://example.com',
  linkDomain: 'your-custom-domain.com', // Use custom Firebase Hosting domain
)

Microsoft Authentication

// Before
final credential = MicrosoftAuthProvider.credential(accessToken);
await FirebaseAuth.instance.signInWithCredential(credential);

// After
final provider = MicrosoftAuthProvider();
await FirebaseAuth.instance.signInWithProvider(provider);

FirebaseAuth Instance

// Before
FirebaseAuth.instanceFor(app: app, persistence: Persistence.local);

// After
final auth = FirebaseAuth.instanceFor(app: app);
auth.setPersistence(Persistence.local);

Email Updates

// Before
await user.updateEmail('[email protected]');

// After
await user.verifyBeforeUpdateEmail('[email protected]');

Email Sign-in Methods

The fetchSignInMethodsForEmail() method has been removed for security reasons. Consider implementing alternative authentication flows that don't require email enumeration.