Add TelephonyManager test hidden API for testing

Test: atest
Bug: 172507765

Change-Id: I30a5b695770509dc803ab5623c75e653d40f4d11

telephony/java/android/telephony/TelephonyManager.java

@@ -13972,6 +13972,15 @@ public class TelephonyManager {
         sServiceHandleCacheEnabled = true;
     }
 
+    /**
+     * Setup sITelephony for testing.
+     * @hide
+     */
+    @VisibleForTesting
+    public static void setupITelephonyForTest(ITelephony telephony) {
+        sITelephony = telephony;
+    }
+
     /**
      * Whether device can connect to 5G network when two SIMs are active.
      * @hide