Qt: Make window corners square on Windows 11 (fixes #3285)

CHANGES

@@ -52,6 +52,7 @@ Misc:
  - Qt: Remove maligned double-click-to-fullscreen shortcut (closes mgba.io/i/2632)
  - Qt: Pass logging context through to video proxy thread (fixes mgba.io/i/3095)
  - Qt: Show maker code and game version in ROM info
+ - Qt: Make window corners square on Windows 11 (fixes mgba.io/i/3285)
  - Res: Port NSO-gba-colors shader (closes mgba.io/i/2834)
  - Scripting: Add `callbacks:oneshot` for single-call callbacks
  - Switch: Add bilinear filtering option (closes mgba.io/i/3111)

src/platform/qt/Window.cpp

@@ -14,6 +14,10 @@
 #include <QScreen>
 #include <QWindow>
 
+#ifdef Q_OS_WIN
+#include <dwmapi.h>
+#endif
+
 #ifdef USE_SQLITE3
 #include "ArchiveInspector.h"
 #include "library/LibraryController.h"
@@ -717,6 +721,11 @@ void Window::showEvent(QShowEvent* event) {
 		return;
 	}
 	m_wasOpened = true;
+#ifdef Q_OS_WIN
+	HWND hwnd = reinterpret_cast<HWND>(winId());
+	DWM_WINDOW_CORNER_PREFERENCE cornerPref = DWMWCP_DONOTROUND;
+	DwmSetWindowAttribute(hwnd, DWMWA_WINDOW_CORNER_PREFERENCE, &cornerPref, sizeof(cornerPref));
+#endif
 	if (m_initialSize.isValid()) {
 		resizeFrame(m_initialSize);
 	}