DolphinQt: Use non-autodismissable menus in menu bar.

A new class that derives from `QMenu` has been introduced. Menus of this
`NonAutodismissibleMenu` type will stay visible when a _checkable_
action is triggered.

This is convenient in menus that feature a series of check boxes that
toggle visibility of third components (e.g. the **List Columns** menu),
allowing the user to toggle several actions at once.

For now, the new type is used in the top menu bar.

Source/Core/DolphinQt/QtUtils/NonAutodismissibleMenu.h

@@ -0,0 +1,22 @@
+// Copyright 2025 Dolphin Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#pragma once
+
+#include <QMenu>
+
+namespace QtUtils
+{
+
+// A menu widget based on QMenu that will not be automatically dismissed when one of its checkable
+// actions are triggered.
+class NonAutodismissibleMenu : public QMenu
+{
+public:
+  using QMenu::QMenu;
+
+protected:
+  void mouseReleaseEvent(QMouseEvent* event) override;
+};
+
+}  // namespace QtUtils