Fix .NET Framework build errors and MAUI Visibility ambiguity

- Add RequiresUnreferencedCodeAttribute polyfill for net462/net472/net481
  targets where the attribute is inaccessible (only public in .NET 5+)
- Add ModuleInitializerAttribute polyfill for benchmark net462 target
- Fix CS0104 Visibility ambiguity in MAUI project on Windows targets by
  using type aliases instead of namespace imports

Author: glennawatson

src/ReactiveUI.Binding.Maui/BooleanToVisibilityTypeConverter.cs

@@ -3,9 +3,9 @@
 // See the LICENSE file in the project root for full license information.
 
 #if WINUI_TARGET
-using Microsoft.UI.Xaml;
+using Visibility = Microsoft.UI.Xaml.Visibility;
 #else
-using Microsoft.Maui;
+using Visibility = Microsoft.Maui.Visibility;
 #endif
 
 namespace ReactiveUI.Binding.Maui;

src/ReactiveUI.Binding.Maui/VisibilityToBooleanTypeConverter.cs

@@ -3,9 +3,9 @@
 // See the LICENSE file in the project root for full license information.
 
 #if WINUI_TARGET
-using Microsoft.UI.Xaml;
+using Visibility = Microsoft.UI.Xaml.Visibility;
 #else
-using Microsoft.Maui;
+using Visibility = Microsoft.Maui.Visibility;
 #endif
 
 namespace ReactiveUI.Binding.Maui;

src/ReactiveUI.Binding/Polyfills/RequiresUnreferencedCodeAttribute.cs

@@ -0,0 +1,51 @@
+// Copyright (c) 2019-2026 ReactiveUI Association Incorporated. All rights reserved.
+// ReactiveUI Association Incorporated licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for full license information.
+
+// Polyfill implementation adapted from SimonCropp/Polyfill
+// https://github.com/SimonCropp/Polyfill
+#if !NET
+
+namespace System.Diagnostics.CodeAnalysis;
+
+/// <summary>
+/// Indicates that the specified method requires dynamic access to code that is not referenced
+/// statically, for example through <see cref="System.Reflection"/>.
+/// </summary>
+/// <remarks>
+/// Link: https://learn.microsoft.com/en-us/dotnet/api/system.diagnostics.codeanalysis.requiresunreferencedcodeattribute.
+/// </remarks>
+[ExcludeFromCodeCoverage]
+[DebuggerNonUserCode]
+[AttributeUsage(
+    AttributeTargets.Method |
+    AttributeTargets.Constructor |
+    AttributeTargets.Class,
+    Inherited = false)]
+internal sealed class RequiresUnreferencedCodeAttribute : Attribute
+{
+    /// <summary>
+    /// Initializes a new instance of the <see cref="RequiresUnreferencedCodeAttribute"/> class
+    /// with the specified message.
+    /// </summary>
+    /// <param name="message">A message that contains information about the usage of unreferenced code.</param>
+    public RequiresUnreferencedCodeAttribute(string message) =>
+        Message = message;
+
+    /// <summary>
+    /// Gets a message that contains information about the usage of unreferenced code.
+    /// </summary>
+    public string Message { get; }
+
+    /// <summary>
+    /// Gets or sets an optional URL that contains more information about the method,
+    /// why it requires unreferenced code, and what options a consumer has to deal with it.
+    /// </summary>
+    public string? Url { get; set; }
+}
+
+#else
+using System.Runtime.CompilerServices;
+
+[assembly: TypeForwardedTo(typeof(System.Diagnostics.CodeAnalysis.RequiresUnreferencedCodeAttribute))]
+#endif

src/benchmarks/ReactiveUI.Binding.Benchmarks.ReactiveUI/Polyfills/ModuleInitializerAttribute.cs

@@ -0,0 +1,25 @@
+// Copyright (c) 2019-2026 ReactiveUI Association Incorporated. All rights reserved.
+// ReactiveUI Association Incorporated licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for full license information.
+
+// Polyfill implementation adapted from SimonCropp/Polyfill
+// https://github.com/SimonCropp/Polyfill
+#if !NET5_0_OR_GREATER
+
+namespace System.Runtime.CompilerServices;
+
+/// <summary>
+/// Used to indicate to the compiler that a method should be called in its containing
+/// module's initializer.
+/// </summary>
+/// <remarks>
+/// When one or more valid methods with this attribute are found in a compilation, the compiler
+/// will emit a module initializer that calls each of the attributed methods.
+/// On .NET Framework this polyfill enables compilation only; the runtime does not invoke module initializers.
+/// </remarks>
+[AttributeUsage(AttributeTargets.Method, Inherited = false)]
+internal sealed class ModuleInitializerAttribute : Attribute
+{
+}
+
+#endif