win: Add HandleToInt() and IntToHandle()

util/win/registration_protocol_win.h

Index: util/win/registration_protocol_win.h
diff --git a/util/win/registration_protocol_win.h b/util/win/registration_protocol_win.h
index a691931d8f84183cc16d5bc70c98c5166342df7a..f2d9e29cfd5b9fad09bab68ed0cc6a99269ed09b 100644
--- a/util/win/registration_protocol_win.h
+++ b/util/win/registration_protocol_win.h
@@ -93,11 +93,6 @@ struct ClientToServerMessage {
 };
 
 //! \brief  A client registration response.
-//!
-//! See <a
-//! href="https://msdn.microsoft.com/en-us/library/windows/desktop/aa384203">Interprocess
-//! Communication Between 32-bit and 64-bit Applications</a> for details on
-//! communicating handle values between processes of varying bitness.
 struct RegistrationResponse {
   //! \brief An event `HANDLE`, valid in the client process, that should be
   //!     signaled to request a crash report. 64-bit clients should convert the