Fixed subscription database cache out of sync

The subscription reloading from database could cause cache
to be out-of-sync. Fixed by making reloading synchronous and
only reload when necessary (e.g. Backup restore actually changes
the database).

Fix: 290295550
Test: atest SubscriptionManagerServiceTest TelephonyProviderTests
Test: Manually test backup/restore
Test: Telephony basic functionality tests
Test: Re-tested passed on b/290295550#comment#23

Change-Id: Ib818110a1f03536ed9082e779b3cc89e56608084

telephony/java/android/telephony/SubscriptionManager.java

@@ -150,6 +150,15 @@ public class SubscriptionManager {
     public static final String RESTORE_SIM_SPECIFIC_SETTINGS_METHOD_NAME =
             "restoreSimSpecificSettings";
 
+    /**
+     * The key of the boolean flag indicating whether restoring subscriptions actually changes
+     * the subscription database or not.
+     *
+     * @hide
+     */
+    public static final String RESTORE_SIM_SPECIFIC_SETTINGS_DATABASE_UPDATED =
+            "restoreSimSpecificSettingsDatabaseUpdated";
+
     /**
      * Key to the backup & restore data byte array in the Bundle that is returned by {@link
      * #getAllSimSpecificSettingsForBackup()} or to be pass in to {@link