Add ParamCollectionAttribute

Author: nike4613

src/MonoMod.Backports/System/Runtime/CompilerServices/ParamCollectionAttribute,gte_core_9.0.cs

@@ -0,0 +1,3 @@
+using System.Runtime.CompilerServices;
+
+[assembly: TypeForwardedTo(typeof(ParamCollectionAttribute))]

src/MonoMod.Backports/System/Runtime/CompilerServices/ParamCollectionAttribute,lt_core_9.0,is_std,is_fx.cs

@@ -0,0 +1,13 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+namespace System.Runtime.CompilerServices
+{
+    /// <summary>
+    /// Indicates that a method will allow a variable number of arguments in its invocation.
+    /// </summary>
+    [AttributeUsage(AttributeTargets.Parameter, Inherited = true, AllowMultiple = false)]
+    public sealed class ParamCollectionAttribute : Attribute
+    {
+    }
+}