DolphinQt: Add function to set a QWidget's window decorations to dark ones on Windows.

Source/Core/DolphinQt/QtUtils/SetWindowDecorations.cpp

@@ -0,0 +1,25 @@
+// Copyright 2023 Dolphin Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#include "DolphinQt/QtUtils/SetWindowDecorations.h"
+
+#include <QWidget>
+
+#include "DolphinQt/Settings.h"
+
+#ifdef _WIN32
+#include <dwmapi.h>
+#endif
+
+void SetQWidgetWindowDecorations(QWidget* widget)
+{
+#ifdef _WIN32
+  if (!Settings::Instance().IsSystemDark())
+    return;
+
+  BOOL use_dark_title_bar = TRUE;
+  DwmSetWindowAttribute(HWND(widget->winId()),
+                        20 /* DWMWINDOWATTRIBUTE::DWMWA_USE_IMMERSIVE_DARK_MODE */,
+                        &use_dark_title_bar, DWORD(sizeof(use_dark_title_bar)));
+#endif
+}