Easy app-installing for Guest users

Allows an admin user to selectively install packages into a Guest user
by displaying a list of available packages that are installed in the
admin, but not in the Guest, and letting the admin choose to copy those
apps to the Guest.

Test: atest SettingsLibTests:com.android.settingslib.users.AppCopyingHelperTest

Test: Manual: install some apps in user 0, create a guest, uninstall
some system apps from it. Now, open this panel. Request some of those
apps be installed in the Guest and verify it worked.

Bug: 193281439

Change-Id: I4e6874a4ee93cd7bba96e1f6c8d04ed95873c1a2
diff --git a/res/xml/app_copier.xml b/res/xml/app_copier.xml
new file mode 100644
index 0000000..d8b4bb8
--- /dev/null
+++ b/res/xml/app_copier.xml
@@ -0,0 +1,20 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!-- Copyright (C) 2021 The Android Open Source Project
+
+     Licensed under the Apache License, Version 2.0 (the "License");
+     you may not use this file except in compliance with the License.
+     You may obtain a copy of the License at
+
+          http://www.apache.org/licenses/LICENSE-2.0
+
+     Unless required by applicable law or agreed to in writing, software
+     distributed under the License is distributed on an "AS IS" BASIS,
+     WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+     See the License for the specific language governing permissions and
+     limitations under the License.
+-->
+
+<PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android"
+                  xmlns:settings="http://schemas.android.com/apk/res-auto"
+                  android:title="@string/user_choose_copy_apps_to_another_user">
+</PreferenceScreen>