WinUI - Test Infra (#3482)

WCT is now sharing WinUI's test infrastructure. This is the continuation of the work on this PR microsoft/microsoft-ui-xaml#3212.

## PR Type
What kind of change does this PR introduce?
- Feature
- Build or CI related changes 

## What is the current behavior?
No UI Tests.

## What is the new behavior?
Added simple UI Tests for the WCT that use the same shared infrastructure used by WinUI. This will enable us to move controls/helpers in an easier way from the WCT->WinUI in the future.

## PR Checklist

Please check if your PR fulfills the following requirements:

- [X] Tested code with current [supported SDKs](../readme.md#supported)
- [ ] Pull Request has been submitted to the documentation repository [instructions](..\contributing.md#docs). Link: <!-- docs PR link -->
- [ ] Sample in sample app has been added / updated (for bug fixes / features)
    - [ ] Icon has been created (if new sample) following the [Thumbnail Style Guide and templates](https://github.com/windows-toolkit/WindowsCommunityToolkit-design-assets)
- [X] Tests for the changes have been added (for bug fixes / features) (if applicable)
- [X] Header has been added to all new source files (run *build/UpdateHeaders.bat*)
- [X] Contains **NO** breaking changes

Author: msftbot[bot]

.gitignore

@@ -227,4 +227,8 @@ msbuild.binlog
 !/build/tools/packages.config
 
 # Generated file from .ttinclude
-**/Generated/TypeInfo.g.cs
+**/Generated/TypeInfo.g.cs
+
+# TAEF Log output
+WexLogFileOutput
+*.wtl

UITests/UITests.App/App.xaml

@@ -0,0 +1,7 @@
+<Application
+    x:Class="UITests.App.App"
+    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+    xmlns:local="using:UITests.App">
+
+</Application>

UITests/UITests.App/App.xaml.cs

@@ -0,0 +1,89 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+using Windows.ApplicationModel;
+using Windows.ApplicationModel.Activation;
+using Windows.UI.Xaml;
+using Windows.UI.Xaml.Controls;
+using Windows.UI.Xaml.Navigation;
+
+namespace UITests.App
+{
+    public sealed partial class App
+    {
+        public App()
+        {
+            this.InitializeComponent();
+            this.Suspending += OnSuspending;
+        }
+
+        /// <summary>
+        /// Invoked when the application is launched normally by the end user.  Other entry points
+        /// will be used such as when the application is launched to open a specific file.
+        /// </summary>
+        /// <param name="e">Details about the launch request and process.</param>
+        protected override void OnLaunched(LaunchActivatedEventArgs e)
+        {
+            Frame rootFrame = Window.Current.Content as Frame;
+
+            // Do not repeat app initialization when the Window already has content,
+            // just ensure that the window is active
+            if (rootFrame == null)
+            {
+                // Create a Frame to act as the navigation context and navigate to the first page
+                rootFrame = new Frame();
+
+                rootFrame.NavigationFailed += OnNavigationFailed;
+
+                if (e.PreviousExecutionState == ApplicationExecutionState.Terminated)
+                {
+                    // TODO: Load state from previously suspended application
+                }
+
+                // Place the frame in the current Window
+                Window.Current.Content = rootFrame;
+            }
+
+            if (e.PrelaunchActivated == false)
+            {
+                if (rootFrame.Content == null)
+                {
+                    // When the navigation stack isn't restored navigate to the first page,
+                    // configuring the new page by passing required information as a navigation
+                    // parameter
+                    rootFrame.Navigate(typeof(MainPage), e.Arguments);
+                }
+
+                // Ensure the current window is active
+                Window.Current.Activate();
+            }
+        }
+
+        /// <summary>
+        /// Invoked when Navigation to a certain page fails
+        /// </summary>
+        /// <param name="sender">The Frame which failed navigation</param>
+        /// <param name="e">Details about the navigation failure</param>
+        private void OnNavigationFailed(object sender, NavigationFailedEventArgs e)
+        {
+            throw new Exception("Failed to load Page " + e.SourcePageType.FullName);
+        }
+
+        /// <summary>
+        /// Invoked when application execution is being suspended.  Application state is saved
+        /// without knowing whether the application will be terminated or resumed with the contents
+        /// of memory still intact.
+        /// </summary>
+        /// <param name="sender">The source of the suspend request.</param>
+        /// <param name="e">Details about the suspend request.</param>
+        private void OnSuspending(object sender, SuspendingEventArgs e)
+        {
+            var deferral = e.SuspendingOperation.GetDeferral();
+
+            // TODO: Save application state and stop any background activity
+            deferral.Complete();
+        }
+    }
+}