Add @hide API to get the phone account handle for a subId.

This is used in SubscriptionManager to figure out which phone account
is being updated when the default voice sub changes.  It seemed like
a good spot to put it since we should really have an api for this in
the future.

Test: Manual, manual, manual
Bug: 128916238
Change-Id: If5137c0e7f01a14810e0ee94e5d857d69f368a87

telephony/java/android/telephony/TelephonyManager.java

@@ -8841,6 +8841,27 @@ public class TelephonyManager {
         return retval;
     }
 
+    /**
+     * Determines the {@link PhoneAccountHandle} associated with a subscription Id.
+     *
+     * @param subscriptionId The subscription Id to check.
+     * @return The {@link PhoneAccountHandle} associated with a subscription Id, or {@code null} if
+     * there is no associated {@link PhoneAccountHandle}.
+     * @hide
+     */
+    public @Nullable PhoneAccountHandle getPhoneAccountHandleForSubscriptionId(int subscriptionId) {
+        PhoneAccountHandle returnValue = null;
+        try {
+            ITelephony service = getITelephony();
+            if (service != null) {
+                returnValue = service.getPhoneAccountHandleForSubscriptionId(subscriptionId);
+            }
+        } catch (RemoteException e) {
+        }
+
+        return returnValue;
+    }
+
     private int getSubIdForPhoneAccountHandle(PhoneAccountHandle phoneAccountHandle) {
         int retval = SubscriptionManager.INVALID_SUBSCRIPTION_ID;
         try {

telephony/java/com/android/internal/telephony/ITelephony.aidl

@@ -1265,6 +1265,11 @@ interface ITelephony {
      */
     int getSubIdForPhoneAccount(in PhoneAccount phoneAccount);
 
+    /**
+     * Returns the PhoneAccountHandle associated with a subscription ID.
+     */
+    PhoneAccountHandle getPhoneAccountHandleForSubscriptionId(int subscriptionId);
+
     void factoryReset(int subId);
 
     /**