Add pretty test for pattern-based Dispose of a ref struct

Only interface-based disposal was covered; a using declaration over
a ref struct with a pattern-based Dispose exercises the recognition
heuristic without IDisposable.

Assisted-by: Claude:claude-fable-5:Claude Code

ICSharpCode.Decompiler.Tests/TestCases/Pretty/UsingVariables.cs

@@ -17,12 +17,25 @@
 // DEALINGS IN THE SOFTWARE.
 
 using System;
+using System.Runtime.InteropServices;
 #if !NET40
 using System.Threading.Tasks;
 #endif
 
 namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 {
+	[StructLayout(LayoutKind.Sequential, Size = 1)]
+	internal ref struct RefStructWithDispose
+	{
+		public void Use()
+		{
+		}
+
+		public void Dispose()
+		{
+		}
+	}
+
 	public class UsingVariables
 	{
 		public IDisposable GetDisposable()
@@ -96,5 +109,13 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 			Use(asyncDisposable);
 		}
 #endif
+
+		public void UsingVarPatternBasedDispose()
+		{
+			Console.WriteLine("before using");
+			using RefStructWithDispose refStructWithDispose = default(RefStructWithDispose);
+			Console.WriteLine("inside using");
+			refStructWithDispose.Use();
+		}
 	}
 }