Address API Council feedback for AppState Datastore.

Added more detailed kdocs to AppStatePreferences API, and renamed `addAppStateToDataStoreListener` to `syncToDataStore`.

Bug: b/552808054
Relnote: Rename `addAppStateToDataStoreListener` to `syncToDataStore`.
Test: Existing
Change-Id: I72bc02df261697c6875f7ade4e1502549cf32229