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.

src/com/android/settings/vpn2/ConfigDialog.java

@@ -16,7 +16,6 @@
 
 package com.android.settings.vpn2;
 
-import android.app.AlertDialog;
 import android.content.Context;
 import android.content.DialogInterface;
 import android.os.Bundle;
@@ -39,6 +38,8 @@ import com.android.settings.R;
 
 import java.net.InetAddress;
 
+import androidx.appcompat.app.AlertDialog;
+
 /**
  * Dialog showing information about a VPN configuration. The dialog
  * can be launched to either edit or prompt for credentials to connect