Fall back to WebBrowser controls when running as admin

The Edge WebView does not at the time of this writing (28. march 2020)
support running in an application with elevated permissions. This commit
adds a test to `WebViewControlHost.IsSupported` which checks if the
application is running as an administrator so that `WebViewCompatible`
will fall back to using the legacy WebBrowser controls.

The tests will unfortunately only work when running the test suite as
administrator, and that will make all the other tests fail.  The test
will therefore be marked as inconclusive instead of failling when the
test suite is running as a non elevated user so that we won't always
have at least one breaking test when we run the test suite.

Tests/UnitTests.WebView.WinForms/FunctionalTests/WebViewCompatible/WebViewCompatibleTests.cs

@@ -0,0 +1,37 @@
+// 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 Microsoft.Toolkit.Win32.UI.Controls.Test.WebView.Shared;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using Should;
+using System.Security.Principal;
+
+namespace Microsoft.Toolkit.Win32.UI.Controls.Test.WinForms.WebView.FunctionalTests.WebViewCompatible
+{
+    [TestClass]
+    public class WebViewCompatibleTests: ContextSpecification
+    {
+        Forms.UI.Controls.WebViewCompatible WebView;
+
+        protected override void Given()
+        {
+            WebView = new Forms.UI.Controls.WebViewCompatible();
+        }
+
+        [TestMethod]
+        public void WebViewCompatibleShouldBeLegacyIfRunningAsAdministrator()
+        {
+            var identity = WindowsIdentity.GetCurrent();
+            var principal = new WindowsPrincipal(identity);
+            if(principal.IsInRole(WindowsBuiltInRole.Administrator))
+            {
+                WebView.IsLegacy.ShouldBeTrue();
+            }
+            else
+            {
+                Assert.Inconclusive("This test needs to be run as administrator");
+            }
+        }
+    }
+}

WebView.Shared/Interop/OSVersionHelper.cs

@@ -5,6 +5,7 @@
 using System;
 using System.IO;
 using System.Security;
+using System.Security.Principal;
 using Microsoft.Toolkit.Win32.UI.Controls.Interop.Win32;
 using Windows.Foundation.Metadata;
 using Windows.Security.EnterpriseData;
@@ -58,6 +59,8 @@ namespace Microsoft.Toolkit.Win32.UI.Controls.Interop
 
         internal static bool IsWindows10 { get; } = IsWindowsNt && IsSince(WindowsVersions.Win10);
 
+        internal static bool IsRunningAsAdministrator { get; } = new WindowsPrincipal(WindowsIdentity.GetCurrent()).IsInRole(WindowsBuiltInRole.Administrator);
+
         /// <summary>
         /// Gets a value indicating whether the current OS is Windows 10 April 2018 Update (Redstone 4) or greater
         /// </summary>

WebView.Shared/Interop/WinRT/WebViewControlHost.cs

@@ -120,7 +120,8 @@ namespace Microsoft.Toolkit.Win32.UI.Controls.Interop.WinRT
 
         internal static bool IsSupported => OSVersionHelper.IsWindows10April2018OrGreater
                                             && OSVersionHelper.IsWorkstation
-                                            && OSVersionHelper.EdgeExists;
+                                            && OSVersionHelper.EdgeExists
+                                            && !OSVersionHelper.IsRunningAsAdministrator;
 
         internal bool CanGoBack
         {