Handle ReferenceKind.RefReadOnly in a few more cases

ICSharpCode.Decompiler/CSharp/CallBuilder.cs

@@ -134,8 +134,7 @@ namespace ICSharpCode.Decompiler.CSharp
 				{
 					if (!useImplicitlyTypedOut)
 						return expression;
-					if (expression.GetResolveResult() is ByReferenceResolveResult brrr
-						&& brrr.IsOut)
+					if (expression.GetResolveResult() is ByReferenceResolveResult { ReferenceKind: ReferenceKind.Out } brrr)
 					{
 						expression.AddAnnotation(UseImplicitlyTypedOutAnnotation.Instance);
 					}

ICSharpCode.Decompiler/CSharp/Resolver/OverloadResolution.cs

@@ -671,8 +671,8 @@ namespace ICSharpCode.Decompiler.CSharp.Resolver
 				{
 					// AllowImplicitIn: `in` parameters can be filled implicitly without `in` DirectionExpression
 					// IsExtensionMethodInvocation: `this ref` and `this in` parameters can be filled implicitly
-					if (((paramRefKind == ReferenceKind.In && AllowImplicitIn)
-						|| (IsExtensionMethodInvocation && parameterIndex == 0 && (paramRefKind == ReferenceKind.In || paramRefKind == ReferenceKind.Ref))
+					if (((paramRefKind is ReferenceKind.In or ReferenceKind.RefReadOnly && AllowImplicitIn)
+						|| (IsExtensionMethodInvocation && parameterIndex == 0 && (paramRefKind is ReferenceKind.In or ReferenceKind.Ref or ReferenceKind.RefReadOnly))
 						) && candidate.ParameterTypes[parameterIndex].SkipModifiers() is ByReferenceType brt)
 					{
 						// Treat the parameter as if it was not declared "in" for the following steps

ICSharpCode.Decompiler/Semantics/ByReferenceResolveResult.cs

@@ -30,9 +30,6 @@ namespace ICSharpCode.Decompiler.Semantics
 	public class ByReferenceResolveResult : ResolveResult
 	{
 		public ReferenceKind ReferenceKind { get; }
-		public bool IsOut => ReferenceKind == ReferenceKind.Out;
-		public bool IsRef => ReferenceKind == ReferenceKind.Ref;
-		public bool IsIn => ReferenceKind == ReferenceKind.In;
 
 		public readonly ResolveResult ElementResult;
 

ICSharpCode.Decompiler/TypeSystem/Implementation/MetadataParameter.cs

@@ -63,7 +63,7 @@ namespace ICSharpCode.Decompiler.TypeSystem.Implementation
 			var metadata = module.metadata;
 			var parameter = metadata.GetParameter(handle);
 
-			bool defaultValueAssignmentAllowed = ReferenceKind is ReferenceKind.None or ReferenceKind.In;
+			bool defaultValueAssignmentAllowed = ReferenceKind is ReferenceKind.None or ReferenceKind.In or ReferenceKind.RefReadOnly;
 
 			if (IsOptional && (!defaultValueAssignmentAllowed || !HasConstantValueInSignature))
 			{