Libraries: Create top level directory for libraries.

Things were getting a little crowded in the project root, so this patch
moves the Lib*/ directories into Libraries/.

Libraries/LibGUI/GMenu.h

@@ -0,0 +1,39 @@
+#pragma once
+
+#include <AK/Function.h>
+#include <AK/RefCounted.h>
+#include <AK/NonnullRefPtr.h>
+#include <AK/Vector.h>
+#include <LibGUI/GMenuItem.h>
+
+class GAction;
+class Point;
+
+class GMenu {
+public:
+    explicit GMenu(const StringView& name);
+    ~GMenu();
+
+    static GMenu* from_menu_id(int);
+
+    GAction* action_at(int);
+
+    void add_action(NonnullRefPtr<GAction>);
+    void add_separator();
+
+    void popup(const Point& screen_position);
+    void dismiss();
+
+    Function<void(unsigned)> on_item_activation;
+
+private:
+    friend class GMenuBar;
+
+    int menu_id() const { return m_menu_id; }
+    int realize_menu();
+    void unrealize_menu();
+
+    int m_menu_id { -1 };
+    String m_name;
+    Vector<OwnPtr<GMenuItem>> m_items;
+};