Make Instruction.GetArgumentType consistent with ParameterList

[ElektroKill]

ParameterList created a GenericInstSig if declaring type is generic, while Instruction.GetArgumentType did not.

dnlib/src/DotNet/ParameterList.cs

Lines 122 to 138 in 8558fa7

	bool isValueType = methodDeclaringType.IsValueType;
	ClassOrValueTypeSig instSig;
	if (isValueType)
	instSig = new ValueTypeSig(methodDeclaringType);
	else
	instSig = new ClassSig(methodDeclaringType);
	TypeSig thisTypeSig;
	if (methodDeclaringType.HasGenericParameters) {
	int gpCount = methodDeclaringType.GenericParameters.Count;
	var genArgs = new List<TypeSig>(gpCount);
	for (int i = 0; i < gpCount; i++)
	genArgs.Add(new GenericVar(i, methodDeclaringType));
	thisTypeSig = new GenericInstSig(instSig, genArgs);
	}
	else
	thisTypeSig = instSig;
	hiddenThisParameter.Type = isValueType ? new ByRefSig(thisTypeSig) : thisTypeSig;

dnlib/src/DotNet/Emit/Instruction.cs

Lines 747 to 748 in 8558fa7

	if (index == 0 && methodSig.ImplicitThis)
	return declaringType?.IsValueType == true ? new ByRefSig(declaringType.ToTypeSig()) : declaringType.ToTypeSig();

if declaringType is TypeSpec we trust the user to provide the proper instantiated type!