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/UserCredentialsSettings.java b/src/com/android/settings/UserCredentialsSettings.java
index 20defb3..06d0be6 100644
--- a/src/com/android/settings/UserCredentialsSettings.java
+++ b/src/com/android/settings/UserCredentialsSettings.java
@@ -18,7 +18,6 @@
 
 import android.annotation.LayoutRes;
 import android.annotation.Nullable;
-import android.app.AlertDialog;
 import android.app.Dialog;
 import android.content.Context;
 import android.content.DialogInterface;
@@ -57,6 +56,7 @@
 import java.util.SortedMap;
 import java.util.TreeMap;
 
+import androidx.appcompat.app.AlertDialog;
 import androidx.fragment.app.DialogFragment;
 import androidx.fragment.app.Fragment;
 import androidx.recyclerview.widget.RecyclerView;