Fix VB -> C# conversion for DefaultMemberAttribute properties

Previously, any property marked with DefaultMemberAttribute was treated as an indexer, causing the property name to be stripped from the C# output. This resulted in invalid C# code for parameterless default properties (e.g., `obj = "val"` instead of `obj.Prop = "val"`). This change ensures that the property name is only stripped if the property actually has parameters (i.e., is a true indexer).

Co-authored-by: GrahamTheCoder <2490482+GrahamTheCoder@users.noreply.github.com>

Author: google-labs-jules[bot]

CodeConverter/CSharp/NameExpressionNodeVisitor.cs

@@ -52,7 +52,7 @@ public async Task<CSharpSyntaxNode> ConvertMemberAccessExpressionAsync(VBasic.Sy
 
         var simpleNameSyntax = await node.Name.AcceptAsync<SimpleNameSyntax>(TriviaConvertingExpressionVisitor);
 
-        var isDefaultProperty = nodeSymbol is IPropertySymbol p && VBasic.VisualBasicExtensions.IsDefault(p);
+        var isDefaultProperty = nodeSymbol is IPropertySymbol p && VBasic.VisualBasicExtensions.IsDefault(p) && p.Parameters.Any();
         ExpressionSyntax left = null;
         if (node.Expression is VBasic.Syntax.MyClassExpressionSyntax && nodeSymbol != null) {
             if (nodeSymbol.IsStatic) {

Tests/CSharp/MemberTests/DefaultMemberAttributeTests.cs

@@ -0,0 +1,55 @@
+using System.Threading.Tasks;
+using ICSharpCode.CodeConverter.Tests.TestRunners;
+using Xunit;
+
+namespace ICSharpCode.CodeConverter.Tests.CSharp.MemberTests;
+
+public class DefaultMemberAttributeTests : ConverterTestBase
+{
+    [Fact]
+    public async Task TestDefaultMemberAttributeConversionAsync()
+    {
+        await TestConversionVisualBasicToCSharpAsync(
+            @"
+<System.Reflection.DefaultMember(""Caption"")>
+Public Class ClassWithReflectionDefaultMember
+    Public Property Caption As String
+End Class
+
+<System.Reflection.DefaultMember(NameOf(LoosingProperties.Caption))>
+Public Class LoosingProperties
+    Public Property Caption As String
+
+    Sub S()
+        Dim x = New LoosingProperties()
+        x.Caption = ""Hello""
+
+        Dim y = New ClassWithReflectionDefaultMember() 'from C#
+        y.Caption = ""World""
+    End Sub
+End Class", @"
+using System.Reflection;
+
+[DefaultMember(""Caption"")]
+public partial class ClassWithReflectionDefaultMember
+{
+    public string Caption { get; set; }
+}
+
+[DefaultMember(nameof(Caption))]
+public partial class LoosingProperties
+{
+    public string Caption { get; set; }
+
+    public void S()
+    {
+        var x = new LoosingProperties();
+        x.Caption = ""Hello"";
+
+        var y = new ClassWithReflectionDefaultMember(); // from C#
+        y.Caption = ""World"";
+    }
+}
+");
+    }
+}