Fix NRT resolution for AIFunction parameters.

eng/MSBuild/LegacySupport.props

@@ -74,4 +74,8 @@
   <ItemGroup Condition="'$(InjectCollectionBuilderAttributesOnLegacy)' == 'true' AND ('$(TargetFramework)' == 'net462' or '$(TargetFramework)' == 'netstandard2.0' or '$(TargetFramework)' == 'netcoreapp3.1')">
     <Compile Include="$(MSBuildThisFileDirectory)\..\..\src\LegacySupport\CollectionBuilder\*.cs" LinkBase="LegacySupport\CollectionBuilder" />
   </ItemGroup>
+
+  <ItemGroup Condition="'$(InjectNullabilityInfoContextOnLegacy)' == 'true' AND ('$(TargetFramework)' == 'net462' or '$(TargetFramework)' == 'netstandard2.0' or '$(TargetFramework)' == 'netcoreapp3.1')">
+    <Compile Include="$(MSBuildThisFileDirectory)\..\..\src\LegacySupport\NullabilityInfoContext\*.cs" LinkBase="LegacySupport\NullabilityInfoContext" />
+  </ItemGroup>
 </Project>

src/LegacySupport/NullabilityInfoContext/NullabilityInfo.cs

@@ -0,0 +1,75 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+#if !NET6_0_OR_GREATER
+using System.Diagnostics.CodeAnalysis;
+
+#pragma warning disable SA1623 // Property summary documentation should match accessors
+
+namespace System.Reflection
+{
+    /// <summary>
+    /// A class that represents nullability info.
+    /// </summary>
+    [ExcludeFromCodeCoverage]
+    internal sealed class NullabilityInfo
+    {
+        internal NullabilityInfo(Type type, NullabilityState readState, NullabilityState writeState,
+            NullabilityInfo? elementType, NullabilityInfo[] typeArguments)
+        {
+            Type = type;
+            ReadState = readState;
+            WriteState = writeState;
+            ElementType = elementType;
+            GenericTypeArguments = typeArguments;
+        }
+
+        /// <summary>
+        /// The <see cref="System.Type" /> of the member or generic parameter
+        /// to which this NullabilityInfo belongs.
+        /// </summary>
+        public Type Type { get; }
+
+        /// <summary>
+        /// The nullability read state of the member.
+        /// </summary>
+        public NullabilityState ReadState { get; internal set; }
+
+        /// <summary>
+        /// The nullability write state of the member.
+        /// </summary>
+        public NullabilityState WriteState { get; internal set; }
+
+        /// <summary>
+        /// If the member type is an array, gives the <see cref="NullabilityInfo" /> of the elements of the array, null otherwise.
+        /// </summary>
+        public NullabilityInfo? ElementType { get; }
+
+        /// <summary>
+        /// If the member type is a generic type, gives the array of <see cref="NullabilityInfo" /> for each type parameter.
+        /// </summary>
+        public NullabilityInfo[] GenericTypeArguments { get; }
+    }
+
+    /// <summary>
+    /// An enum that represents nullability state.
+    /// </summary>
+    internal enum NullabilityState
+    {
+        /// <summary>
+        /// Nullability context not enabled (oblivious).
+        /// </summary>
+        Unknown,
+
+        /// <summary>
+        /// Non nullable value or reference type.
+        /// </summary>
+        NotNull,
+
+        /// <summary>
+        /// Nullable value or reference type.
+        /// </summary>
+        Nullable,
+    }
+}
+#endif