Cleanup VARIANT marshalling and convert to managed

src/coreclr/System.Private.CoreLib/System.Private.CoreLib.csproj

@@ -286,6 +286,9 @@
     <Compile Include="$(CommonPath)Interop\Windows\OleAut32\Interop.VariantClear.cs">
       <Link>Common\Interop\Windows\OleAut32\Interop.VariantClear.cs</Link>
     </Compile>
+    <Compile Include="$(CommonPath)Interop\Windows\OleAut32\Interop.VariantChangeTypeEx.cs">
+      <Link>Common\Interop\Windows\OleAut32\Interop.VariantChangeTypeEx.cs</Link>
+    </Compile>
   </ItemGroup>
   <ItemGroup Condition="'$(FeatureObjCMarshal)' == 'true'">
     <Compile Include="$(BclSourcesRoot)\System\Runtime\InteropServices\ObjectiveCMarshal.CoreCLR.cs" />

src/coreclr/System.Private.CoreLib/src/Microsoft/Win32/OAVariantLib.cs

@@ -151,19 +151,10 @@ private static ComVariant ToOAVariant(object input)
                 null => default,
                 Missing => throw new NotSupportedException(SR.NotSupported_ChangeType),
                 DBNull => ComVariant.Null,
-                _ => GetComIPFromObjectRef(input) // Convert the object to an IDispatch/IUnknown pointer.
+                _ => Variant.GetIUnknownOrIDispatchFromObject(input) // Convert the object to an IDispatch/IUnknown pointer.
             };
         }
 
-        private static ComVariant GetComIPFromObjectRef(object? obj)
-        {
-            IntPtr pUnk = GetIUnknownOrIDispatchForObject(ObjectHandleOnStack.Create(ref obj), out bool isIDispatch);
-            return ComVariant.CreateRaw(isIDispatch ? VarEnum.VT_DISPATCH : VarEnum.VT_UNKNOWN, pUnk);
-        }
-
-        [LibraryImport(RuntimeHelpers.QCall, EntryPoint = "MarshalNative_GetIUnknownOrIDispatchForObject")]
-        private static partial IntPtr GetIUnknownOrIDispatchForObject(ObjectHandleOnStack o, [MarshalAs(UnmanagedType.Bool)] out bool isIDispatch);
-
         private static object? FromOAVariant(ComVariant input) =>
             input.VarType switch
             {