Add CoCreateInstance overload that gives intptr.

src/Windows/Avalonia.Win32/Interop/UnmanagedMethods.cs

@@ -1147,7 +1147,10 @@ namespace Avalonia.Win32.Interop
         internal static extern int CoCreateInstance(ref Guid clsid,
             IntPtr ignore1, int ignore2, ref Guid iid, [MarshalAs(UnmanagedType.IUnknown), Out] out object pUnkOuter);
 
-        
+        [DllImport("ole32.dll", PreserveSig = true)]
+        internal static extern int CoCreateInstance(ref Guid clsid,
+            IntPtr ignore1, int ignore2, ref Guid iid, [Out] out IntPtr pUnkOuter);
+
         [DllImport("shell32.dll", CharSet = CharSet.Unicode, SetLastError = true)]
         internal static extern int SHCreateItemFromParsingName([MarshalAs(UnmanagedType.LPWStr)] string pszPath, IntPtr pbc, ref Guid riid, [MarshalAs(UnmanagedType.Interface)] out IShellItem ppv);