NativeWindow AssignHandle/ReleaseHandle should use Set/RemoveWindowSubclass

`NativeWindow AssignHandle/ReleaseHandle` use `SetWindowLongPtr` to subclass windows. This is particularly problematic if multiple independent components subclass the same window, as described here:

https://blogs.msdn.microsoft.com/anandgeorge/2010/04/10/usage-of-nativewindow-assignhandlereleasehandle-when-unmanaged-code-is-involved/

Our Office add-in coexists with other .NET add-ins and frequently runs into this problem. To solve it, `NativeWindow` should use the `COMCTL32` `SetWindowSubclass`/`RemoveWindowSubclass` API.