feat(firestore)!: remove deprecated functions

[Lyokone]

Summary

Removes all deprecated methods from the cloud_firestore package's front-facing API in preparation for a breaking change release.

Removed Methods

• databaseURL parameter/property → Use databaseId instead
• enablePersistence() method → Use Settings.persistenceEnabled instead
• setIndexConfiguration() method → Use PersistentCacheIndexManager instead
• enableIndexedDbPersistence() function → Use FirestoreSettings.localCache instead
• cacheSizeBytes setter → Use FirestoreSettings.localCache instead

Migration Guide

// Before FirebaseFirestore.instanceFor(app: app, databaseURL: 'db'); await firestore.enablePersistence(); await firestore.setIndexConfiguration(indexes: [...]); // After  FirebaseFirestore.instanceFor(app: app, databaseId: 'db'); firestore.settings = const Settings(persistenceEnabled: true); final indexManager = firestore.persistentCacheIndexManager(); await indexManager?.enableIndexAutoCreation();

[russellwheatley]

Need CI fixing on this one