FIx - Add ReactiveFlyoutPage to Maui (#3720)

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[Contribute](https://github.com/reactiveui/reactiveui#contribute)
section of the README -->

**What kind of change does this PR introduce?**
<!-- Bug fix, feature, docs update, ... -->

FIx for #3719 

**What is the current behavior?**
<!-- You can also link to an open issue here. -->

Maui is missing ReactiveFlyoutPage 

**What is the new behavior?**
<!-- If this is a feature change -->

Added ReactiveFlyoutPage to Maui
Updated Verify.Xunit and made code changes as required.

**What might this PR break?**

None

**Please check if the PR fulfills these requirements**
- [ ] Tests for the changes have been added (for bug fixes / features)
- [ ] Docs have been added / updated (for bug fixes / features)

**Other information**:

src/Directory.build.props

@@ -33,7 +33,7 @@
     <EmbedUntrackedSources>true</EmbedUntrackedSources>
     <IncludePackageReferencesDuringMarkupCompilation>true</IncludePackageReferencesDuringMarkupCompilation>
     <PublishRepositoryUrl>true</PublishRepositoryUrl>
-    <XunitVersion>2.6.4</XunitVersion>
+    <XunitVersion>2.6.6</XunitVersion>
   </PropertyGroup>
   <!--<PropertyGroup Condition="$(IsTestProject) != 'true'">
     <TreatWarningsAsErrors>true</TreatWarningsAsErrors>
@@ -58,7 +58,7 @@
     <PackageReference Include="Microsoft.Reactive.Testing" Version="6.0.0" />
     <PackageReference Include="PublicApiGenerator" Version="11.1.0" />
     <PackageReference Include="coverlet.msbuild" Version="6.0.0" PrivateAssets="All" />
-    <PackageReference Include="Verify.Xunit" Version="22.11.1" />
+    <PackageReference Include="Verify.Xunit" Version="23.0.1" />
   </ItemGroup>
 
   <ItemGroup Condition="'$(IsTestProject)' != 'true'">

src/ReactiveUI.Fody.Tests/API/ApiApprovalTests.cs

@@ -7,7 +7,6 @@
 using System.Threading.Tasks;
 using ReactiveUI.Fody.Helpers;
 using ReactiveUI.Tests;
-using VerifyXunit;
 using Xunit;
 
 namespace ReactiveUI.Fody.Tests.API;
@@ -19,7 +18,6 @@ namespace ReactiveUI.Fody.Tests.API;
 /// for version changing reasons.
 /// </summary>
 [ExcludeFromCodeCoverage]
-[UsesVerify]
 public class ApiApprovalTests
 {
     /// <summary>

src/ReactiveUI.Fody.Tests/ApiExtensions.cs

@@ -17,7 +17,6 @@ namespace ReactiveUI.Tests;
 /// A helper for doing API approvals.
 /// </summary>
 [ExcludeFromCodeCoverage]
-[UsesVerify]
 public static class ApiExtensions
 {
     /// <summary>

src/ReactiveUI.Maui/ReactiveFlyoutPage.cs

@@ -0,0 +1,54 @@
+// Copyright (c) 2023 .NET Foundation and Contributors. All rights reserved.
+// 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 full license information.
+
+using Microsoft.Maui.Controls;
+
+namespace ReactiveUI.Maui;
+
+/// <summary>
+/// Reactive Flyout Page.
+/// </summary>
+/// <typeparam name="TViewModel">The type of the view model.</typeparam>
+/// <seealso cref="FlyoutPage" />
+/// <seealso cref="IViewFor{TViewModel}" />
+public class ReactiveFlyoutPage<TViewModel> : FlyoutPage, IViewFor<TViewModel>
+    where TViewModel : class
+{
+    /// <summary>
+    /// The view model bindable property.
+    /// </summary>
+    public static readonly BindableProperty ViewModelProperty = BindableProperty.Create(
+     nameof(ViewModel),
+     typeof(TViewModel),
+     typeof(ReactiveFlyoutPage<TViewModel>),
+     default(TViewModel),
+     BindingMode.OneWay,
+     propertyChanged: OnViewModelChanged);
+
+    /// <summary>
+    /// Gets or sets the ViewModel to display.
+    /// </summary>
+    public TViewModel? ViewModel
+    {
+        get => (TViewModel)GetValue(ViewModelProperty);
+        set => SetValue(ViewModelProperty, value);
+    }
+
+    /// <inheritdoc/>
+    object? IViewFor.ViewModel
+    {
+        get => ViewModel;
+        set => ViewModel = (TViewModel?)value;
+    }
+
+    /// <inheritdoc/>
+    protected override void OnBindingContextChanged()
+    {
+        base.OnBindingContextChanged();
+        ViewModel = BindingContext as TViewModel;
+    }
+
+    private static void OnViewModelChanged(BindableObject bindableObject, object oldValue, object newValue) => bindableObject.BindingContext = newValue;
+}

src/ReactiveUI.Tests/API/ApiApprovalTests.cs

@@ -3,15 +3,12 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for full license information.
 
-using VerifyXunit;
-
 namespace ReactiveUI.Tests.API;
 
 /// <summary>
 /// Checks to make sure that the API is consistent with previous releases, and new API changes are highlighted.
 /// </summary>
 [ExcludeFromCodeCoverage]
-[UsesVerify]
 public class ApiApprovalTests
 {
     /// <summary>

src/ReactiveUI.Tests/Platforms/windows-xaml/Api/XamlApiApprovalTests.cs

@@ -3,15 +3,12 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for full license information.
 
-using VerifyXunit;
-
 namespace ReactiveUI.Tests.Xaml;
 
 /// <summary>
 /// API approvals for the xaml project.
 /// </summary>
 [ExcludeFromCodeCoverage]
-[UsesVerify]
 public class XamlApiApprovalTests
 {
     /// <summary>

src/ReactiveUI.Tests/Platforms/winforms/API/WinformsApiApprovalTests.cs

@@ -3,15 +3,12 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for full license information.
 
-using VerifyXunit;
-
 namespace ReactiveUI.Tests;
 
 /// <summary>
 /// Checks the WinForms API to make sure there aren't any unexpected public API changes.
 /// </summary>
 [ExcludeFromCodeCoverage]
-[UsesVerify]
 public class WinformsApiApprovalTests
 {
     /// <summary>

src/ReactiveUI.Tests/Platforms/wpf/API/WpfApiApprovalTests.cs

@@ -3,15 +3,12 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for full license information.
 
-using VerifyXunit;
-
 namespace ReactiveUI.Tests.Wpf;
 
 /// <summary>
 /// Checks the WPF API to make sure there aren't any unexpected public API changes.
 /// </summary>
 [ExcludeFromCodeCoverage]
-[UsesVerify]
 public class WpfApiApprovalTests
 {
     /// <summary>

src/ReactiveUI.Tests/Utilities/ApiExtensions.cs

@@ -16,7 +16,6 @@ namespace ReactiveUI.Tests;
 /// A helper for doing API approvals.
 /// </summary>
 [ExcludeFromCodeCoverage]
-[UsesVerify]
 public static class ApiExtensions
 {
     /// <summary>