Merge bitcoin-core/gui#789: Avoid non-self-contained Windows header

8023640 qt: Avoid non-self-contained Windows header (Hennadii Stepanov)

Pull request description:

  Using the `windows.h` header guarantees correctness regardless of the content of other headers.

  For more details, please refer to https://stackoverflow.com/questions/4845198/fatal-error-no-target-architecture-in-visual-studio

  Fixes the MSVC build when using the upcoming CMake-based build system and Qt packages installed via the vcpkg package manager.

  Related to hebasto#77.

ACKs for top commit:
  theuni:
    ACK 8023640. It's not completely clear to me why this currently works, but I don't think it's worth wasting more time on. `windows.h` seems more correct regardless.

Tree-SHA512: 1c03f909943111fb2663f86d33ec9a947bc5903819e5bd94f436f6b0782d9f5c5d80d9cd3490674ecd8921b2981c509e97e41580bccc436f8b5c7db84b4e493c

src/qt/winshutdownmonitor.h

@@ -9,7 +9,7 @@
 #include <QByteArray>
 #include <QString>
 
-#include <windef.h> // for HWND
+#include <windows.h>
 
 #include <QAbstractNativeEventFilter>