Make generic composition details relative addresses

I'm looking at size regressions between .NET Native 1.7 and the current mainline branch. A thing that stood out is universally bigger EETypes. A contributor to this was getting rid of GenericInstanceDescs between 1.7 and 2.0 and replacing them by direct references to generic composition details from the EEType. Size-wise, this was mostly a wash, but we can actually do better - these new fields are not critical to be pointer-sized.
This change turns them into relative pointers. This saves 33 kB on a hello world app. I expect around 100 kB savings on the UWP People app based on my back-of-the-envelope calculation.

Project N baggage:
1. Update pntestcl build configuration to compile it with a C# compiler that is not 8 years old
2. Disable metadata validation transform on class libraries. This is hitting what appears to be a CCI metadata validator bug (Validator.cs:796) where it thinks a modified type should have the same interned key as the unmodified version of it. The act of resolving a modified type strips off the modifier. This ticks off the validator.
3. Fix a Reducer bug where it wasn't marking non-interface constraints as necessary. The C# unmanaged constraint is expressed as [modreq UnmanagedType] ValueType. We were not marking UnmanagedType as necessary.
4. Update checked in binder because this is a file format change

[tfs-changeset: 1708263]

3 files changed, 34 insertions, 1 deletions

diff --git a/src/Runtime.Base/src/Internal/Runtime/CompilerServices/Unsafe.cs b/src/Runtime.Base/src/Internal/Runtime/CompilerServices/Unsafe.cs
index 705193a3c..c63760b39 100644
--- a/src/Runtime.Base/src/Internal/Runtime/CompilerServices/Unsafe.cs
+++ b/src/Runtime.Base/src/Internal/Runtime/CompilerServices/Unsafe.cs
@@ -21,8 +21,22 @@ namespace Internal.Runtime.CompilerServices
     /// <summary>
     /// Contains generic, low-level functionality for manipulating pointers.
     /// </summary>
-    public static class Unsafe
+    public static unsafe class Unsafe
     {
+        /// <summary>
+        /// Returns a pointer to the given by-ref parameter.
+        /// </summary>
+        [Intrinsic]
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static void* AsPointer<T>(ref T value)
+        {
+            throw new PlatformNotSupportedException();
+
+            // ldarg.0
+            // conv.u
+            // ret
+        }
+
         [Intrinsic]
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         public static int SizeOf<T>()
@@ -83,5 +97,15 @@ namespace Internal.Runtime.CompilerServices
         {
             return ref AddByteOffset(ref source, (IntPtr)(elementOffset * (nint)SizeOf<T>()));
         }
+
+        /// <summary>
+        /// Reinterprets the given location as a reference to a value of type <typeparamref name="T"/>.
+        /// </summary>
+        [Intrinsic]
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static ref T AsRef<T>(in T source)
+        {
+            throw new PlatformNotSupportedException();
+        }
     }
 }
diff --git a/src/Runtime.Base/src/Runtime.Base.csproj b/src/Runtime.Base/src/Runtime.Base.csproj
index daa602215..58d17c3b9 100644
--- a/src/Runtime.Base/src/Runtime.Base.csproj
+++ b/src/Runtime.Base/src/Runtime.Base.csproj
@@ -77,6 +77,7 @@
     <Compile Include="System\Runtime\CompilerServices\MethodImplAttribute.cs" />
     <Compile Include="System\Runtime\CompilerServices\RuntimeHelpers.cs" />
     <Compile Include="System\Runtime\CompilerServices\UnsafeValueTypeAttribute.cs" />
+    <Compile Include="System\Runtime\InteropServices\UnmanagedType.cs" />
     <Compile Include="System\Runtime\InteropServices\CallingConvention.cs" />
     <Compile Include="System\Runtime\InteropServices\CharSet.cs" />
     <Compile Include="System\Runtime\InteropServices\DllImportAttribute.cs" />
diff --git a/src/Runtime.Base/src/System/Runtime/InteropServices/UnmanagedType.cs b/src/Runtime.Base/src/System/Runtime/InteropServices/UnmanagedType.cs
new file mode 100644
index 000000000..143ed33c0
--- /dev/null
+++ b/src/Runtime.Base/src/System/Runtime/InteropServices/UnmanagedType.cs
@@ -0,0 +1,8 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+namespace System.Runtime.InteropServices
+{
+    internal class UnmanagedType { }
+}