Flutter Firestore offline setup uses depreciate code

[srivats22]

In the Flutter Firestore Plugin Using the following code:

await db
        .enablePersistence(const PersistenceSettings(synchronizeTabs: true));

Throws a warning saying enablePersistence is depreciated and should use persistenceEnabled.

https://github.com/firebase/snippets-flutter/blob/0428b747c6033ef1f5e27d65e64bb6ed2d533bda/packages/firebase_snippets_app/lib/snippets/firestore.dart#L1072-L1077

Can the document be updated to reflect this? I can submit a PR for the same if that's ok.