Add Unit Test for NotificationMgr

-Make NotificationMgr constructor package private
-Cover UT cases for all supported notifications.

Bug: 242451629
Test: atest NotificationMgrTest
Change-Id: I49395b7ddeb2a933fc92287c251de43e659ce819
diff --git a/src/com/android/phone/NotificationMgr.java b/src/com/android/phone/NotificationMgr.java
index f2641a1..b9d1f53 100644
--- a/src/com/android/phone/NotificationMgr.java
+++ b/src/com/android/phone/NotificationMgr.java
@@ -57,6 +57,7 @@
 import android.util.SparseArray;
 import android.widget.Toast;
 
+import com.android.internal.annotations.VisibleForTesting;
 import com.android.internal.telephony.Phone;
 import com.android.internal.telephony.PhoneFactory;
 import com.android.internal.telephony.TelephonyCapabilities;
@@ -163,7 +164,8 @@
      * Private constructor (this is a singleton).
      * @see #init(PhoneGlobals)
      */
-    private NotificationMgr(PhoneGlobals app) {
+    @VisibleForTesting
+    /* package */ NotificationMgr(PhoneGlobals app) {
         mApp = app;
         mContext = app;
         mStatusBarManager =