Migrate all AlertDialogs to AndroidX version

This CL only changed AlertDialog imports.
So, reviewer can review it easily.

Change-Id: I097bc44394195b14287f4f920c570ac8653f356a
Fixes: 111413092
Test: This CL can't pass Robo test.
diff --git a/src/com/android/settings/BandMode.java b/src/com/android/settings/BandMode.java
index b130295..9728a5f 100644
--- a/src/com/android/settings/BandMode.java
+++ b/src/com/android/settings/BandMode.java
@@ -1,7 +1,6 @@
 package com.android.settings;
 
 import android.app.Activity;
-import android.app.AlertDialog;
 import android.content.DialogInterface;
 import android.os.AsyncResult;
 import android.os.Bundle;
@@ -18,6 +17,7 @@
 import com.android.internal.telephony.Phone;
 import com.android.internal.telephony.PhoneFactory;
 
+import androidx.appcompat.app.AlertDialog;
 
 /**
  * Radio Band Mode Selection Class