Expose nullability info (#54985)

* Expose nullability info from Reflection

src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems

@@ -615,6 +615,8 @@
     <Compile Include="$(MSBuildThisFileDirectory)System\Reflection\Missing.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Reflection\Module.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Reflection\ModuleResolveEventHandler.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)System\Reflection\NullabilityInfo.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)System\Reflection\NullabilityInfoContext.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Reflection\ObfuscateAssemblyAttribute.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Reflection\ObfuscationAttribute.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Reflection\ParameterAttributes.cs" />
@@ -2319,4 +2321,4 @@
     <Compile Include="$(MSBuildThisFileDirectory)System\IUnaryNegationOperators.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\IUnaryPlusOperators.cs" />
   </ItemGroup>
-</Project>
+</Project>

src/libraries/System.Private.CoreLib/src/System/Reflection/NullabilityInfo.cs

@@ -0,0 +1,64 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Collections.ObjectModel;
+
+namespace System.Reflection
+{
+    /// <summary>
+    /// A class that represents nullability info
+    /// </summary>
+    public 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>
+    public 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
+    }
+}