LibGUI: Make Action::set_text() update any associated menu items

Now you can change the text of an action and it will actually show
up in the menu. :^)

Userland/Libraries/LibGUI/Action.cpp

@@ -343,4 +343,14 @@ void Action::set_icon(const Gfx::Bitmap* icon)
     m_icon = icon;
 }
 
+void Action::set_text(String text)
+{
+    if (m_text == text)
+        return;
+    m_text = move(text);
+    for_each_menu_item([&](auto& menu_item) {
+        menu_item.update_from_action({});
+    });
+}
+
 }

Userland/Libraries/LibGUI/Action.h

@@ -66,7 +66,7 @@ public:
     virtual ~Action() override;
 
     String text() const { return m_text; }
-    void set_text(String text) { m_text = move(text); }
+    void set_text(String);
 
     String const& status_tip() const { return m_status_tip; }
     void set_status_tip(String status_tip) { m_status_tip = move(status_tip); }

Userland/Libraries/LibGUI/MenuItem.h

@@ -50,6 +50,8 @@ public:
     void set_menu_id(Badge<Menu>, unsigned menu_id);
     void set_identifier(Badge<Menu>, unsigned identifier);
 
+    void update_from_action(Badge<Action>) { update_window_server(); }
+
 private:
     void update_window_server();