Remove obsolete lifetime annotation fields

ScopedKind is now the authoritative lifetime representation, so retaining
the preview-era boolean fields would duplicate state. Keep the current
ScopedRef compatibility property and group the new metadata attributes
with the other C# 11 attributes.

Assisted-by: Copilot:gpt-5.6-sol:GitHub Copilot CLI
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Copilot-Session: 86d2918e-5a24-48b4-9a86-41d331ec3720

ICSharpCode.Decompiler/TypeSystem/IParameter.cs

@@ -18,7 +18,6 @@
 
 #nullable enable
 
-using System;
 using System.Collections.Generic;
 using System.Runtime.CompilerServices;
 
@@ -52,23 +51,7 @@ namespace ICSharpCode.Decompiler.TypeSystem
 		/// Gets or sets the scope explicitly encoded by <c>ScopedRefAttribute</c>.
 		/// Implicit and redundant scopedness is excluded.
 		/// </summary>
-		public ScopedKind DeclaredScope {
-			get {
-#pragma warning disable 618
-				if (ValueScoped)
-					return ScopedKind.ScopedValue;
-				if (RefScoped)
-					return ScopedKind.ScopedRef;
-#pragma warning restore 618
-				return ScopedKind.None;
-			}
-			set {
-#pragma warning disable 618
-				RefScoped = value != ScopedKind.None;
-				ValueScoped = value == ScopedKind.ScopedValue;
-#pragma warning restore 618
-			}
-		}
+		public ScopedKind DeclaredScope { get; set; }
 
 		/// <summary>
 		/// C# 11 scoped annotation: "scoped ref" (ScopedRefAttribute)
@@ -78,12 +61,6 @@ namespace ICSharpCode.Decompiler.TypeSystem
 			set { DeclaredScope = value ? ScopedKind.ScopedRef : ScopedKind.None; }
 		}
 
-		[Obsolete("Use ScopedRef property instead of directly accessing this field")]
-		public bool RefScoped;
-
-		[Obsolete("C# 11 preview: \"ref scoped\" no longer supported")]
-		public bool ValueScoped;
-
 		/// <summary>
 		/// Gets or sets whether <c>UnscopedRefAttribute</c> is present.
 		/// </summary>

ICSharpCode.Decompiler/TypeSystem/Implementation/KnownAttributes.cs

@@ -114,21 +114,19 @@ namespace ICSharpCode.Decompiler.TypeSystem
 
 		// C# 11 attributes:
 		Required,
+		UnscopedRef,
+		RefSafetyRules,
 
 		// C# 12 attributes:
 		InlineArray,
 
 		// C# 14 attributes:
 		ExtensionMarker,
-
-		// Lifetime attributes:
-		UnscopedRef,
-		RefSafetyRules,
 	}
 
 	public static class KnownAttributes
 	{
-		internal const int Count = (int)KnownAttribute.RefSafetyRules + 1;
+		internal const int Count = (int)KnownAttribute.ExtensionMarker + 1;
 
 		static readonly TopLevelTypeName[] typeNames = new TopLevelTypeName[Count]{
 			default,
@@ -200,13 +198,12 @@ namespace ICSharpCode.Decompiler.TypeSystem
 			new TopLevelTypeName("System.Runtime.InteropServices", "UnmanagedCallersOnlyAttribute"),
 			// C# 11 attributes:
 			new TopLevelTypeName("System.Runtime.CompilerServices", "RequiredMemberAttribute"),
+			new TopLevelTypeName("System.Diagnostics.CodeAnalysis", "UnscopedRefAttribute"),
+			new TopLevelTypeName("System.Runtime.CompilerServices", "RefSafetyRulesAttribute"),
 			// C# 12 attributes:
 			new TopLevelTypeName("System.Runtime.CompilerServices", "InlineArrayAttribute"),
 			// C# 14 attributes:
 			new TopLevelTypeName("System.Runtime.CompilerServices", "ExtensionMarkerAttribute"),
-			// Lifetime attributes:
-			new TopLevelTypeName("System.Diagnostics.CodeAnalysis", "UnscopedRefAttribute"),
-			new TopLevelTypeName("System.Runtime.CompilerServices", "RefSafetyRulesAttribute"),
 		};
 
 		public static ref readonly TopLevelTypeName GetTypeName(this KnownAttribute attr)