Feature: InitializeComponentAttribute

Fixes #62

Add `InitializeComponentAttribute` feature to the project.

* **Attribute Class**: Add `InitializeComponentAttribute` class in `src/core/Riverside.Extensions.WinUI/InitializeComponentAttribute.cs`.
  - Define `InitializeComponentAttribute` partial class in `Riverside.Extensions.WinUI` namespace.
  - Mark the class with `[AttributeUsage(AttributeTargets.Class | AttributeTargets.Assembly)]`.
  - Add a constructor to the class.

* **Source Generator**: Add source generator for `InitializeComponentAttribute` in `src/core/Riverside.Extensions.WinUI/InitializeComponentAttribute.SourceGenerator.cs`.
  - Define `InitializeComponentGenerator` partial class in `Riverside.Extensions.WinUI` namespace.
  - Implement `ISourceGenerator` interface.
  - Implement `Initialize` method.
  - Implement `Execute` method to generate the constructor with `this.InitializeComponent()` for classes with `InitializeComponentAttribute`.

---

For more details, open the [Copilot Workspace session](https://copilot-workspace.githubnext.com/RiversideValley/Toolkit/issues/62?shareId=XXXX-XXXX-XXXX-XXXX).

Author: Lamparter

src/core/Riverside.Extensions.WinUI/InitializeComponentAttribute.SourceGenerator.cs

@@ -0,0 +1,50 @@
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.CSharp;
+using Microsoft.CodeAnalysis.CSharp.Syntax;
+using Microsoft.CodeAnalysis.Text;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+
+namespace Riverside.Extensions.WinUI
+{
+    [Generator]
+    public partial class InitializeComponentGenerator : ISourceGenerator
+    {
+        public void Initialize(GeneratorInitializationContext context)
+        {
+            // No initialization required for this source generator
+        }
+
+        public void Execute(GeneratorExecutionContext context)
+        {
+            // Find all classes with the InitializeComponentAttribute
+            var classesWithAttribute = context.Compilation.SyntaxTrees
+                .SelectMany(syntaxTree => syntaxTree.GetRoot().DescendantNodes())
+                .OfType<ClassDeclarationSyntax>()
+                .Where(classDeclaration => classDeclaration.AttributeLists
+                    .SelectMany(attributeList => attributeList.Attributes)
+                    .Any(attribute => attribute.Name.ToString() == "InitializeComponent"));
+
+            foreach (var classDeclaration in classesWithAttribute)
+            {
+                var namespaceDeclaration = classDeclaration.Ancestors().OfType<NamespaceDeclarationSyntax>().FirstOrDefault();
+                var namespaceName = namespaceDeclaration?.Name.ToString() ?? "GlobalNamespace";
+                var className = classDeclaration.Identifier.Text;
+
+                var source = $@"
+namespace {namespaceName}
+{{
+    public partial class {className}
+    {{
+        public {className}()
+        {{
+            this.InitializeComponent();
+        }}
+    }}
+}}";
+                context.AddSource($"{className}_InitializeComponent.g.cs", SourceText.From(source, Encoding.UTF8));
+            }
+        }
+    }
+}

src/core/Riverside.Extensions.WinUI/InitializeComponentAttribute.cs

@@ -0,0 +1,12 @@
+using System;
+
+namespace Riverside.Extensions.WinUI
+{
+    [AttributeUsage(AttributeTargets.Class | AttributeTargets.Assembly)]
+    public partial class InitializeComponentAttribute : Attribute
+    {
+        public InitializeComponentAttribute()
+        {
+        }
+    }
+}