.NET Workflows - Add support for tool approval (#1685)

* Draft

* Nullable init

* Complete

* Consistency

* Test fix

* Typo

* Comment

* Updated

* Fix identifier

* Test fix

* Comment typo

* Better naming

* Comment

* Tweak comment

dotnet/tests/Microsoft.Agents.AI.Workflows.Declarative.UnitTests/Events/UserMessageRequestTest.cs

@@ -0,0 +1,22 @@
+// Copyright (c) Microsoft. All rights reserved.
+
+using Microsoft.Agents.AI.Workflows.Declarative.Events;
+using Xunit.Abstractions;
+
+namespace Microsoft.Agents.AI.Workflows.Declarative.UnitTests.Events;
+
+/// <summary>
+/// Verify <see cref="AnswerRequest"/> class
+/// </summary>
+public sealed class UserMessageRequestTest(ITestOutputHelper output) : EventTest(output)
+{
+    [Fact]
+    public void VerifySerialization()
+    {
+        // Arrange & Act
+        AnswerRequest copy = VerifyEventSerialization(new AnswerRequest("wassup"));
+
+        // Assert
+        Assert.Equal("wassup", copy.Prompt);
+    }
+}