LibGUI+WindowServer: Flash menubar menu when using a keyboard shortcut

Briefly flash the menubar menu containing the keyboard shortcut action
to give the user immediate visual feedback on their interaction with the
system.

Userland/Libraries/LibGUI/Action.cpp

@@ -135,6 +135,14 @@ void Action::activate(Core::Object* activator)
     m_activator = nullptr;
 }
 
+void Action::flash_menubar_menu()
+{
+    if (auto* app = Application::the())
+        if (auto* window = app->active_window())
+            for (auto& menu_item : m_menu_items)
+                window->flash_menubar_menu_for(*menu_item);
+}
+
 void Action::register_button(Badge<Button>, Button& button)
 {
     m_buttons.set(&button);

Userland/Libraries/LibGUI/Action.h

@@ -92,6 +92,7 @@ public:
     Function<void(Action&)> on_activation;
 
     void activate(Core::Object* activator = nullptr);
+    void flash_menubar_menu();
 
     bool is_enabled() const { return m_enabled; }
     void set_enabled(bool);

Userland/Libraries/LibGUI/MenuItem.h

@@ -48,6 +48,7 @@ public:
     bool is_default() const { return m_default; }
     void set_default(bool);
 
+    int menu_id() const { return m_menu_id; }
     void set_menu_id(Badge<Menu>, unsigned menu_id);
     void set_identifier(Badge<Menu>, unsigned identifier);
 

Userland/Libraries/LibGUI/Window.cpp

@@ -16,6 +16,7 @@
 #include <LibGUI/Application.h>
 #include <LibGUI/Desktop.h>
 #include <LibGUI/Event.h>
+#include <LibGUI/MenuItem.h>
 #include <LibGUI/Menubar.h>
 #include <LibGUI/Painter.h>
 #include <LibGUI/Widget.h>
@@ -1204,6 +1205,15 @@ Menu& Window::add_menu(String name)
     return *menu;
 }
 
+void Window::flash_menubar_menu_for(const MenuItem& menu_item)
+{
+    auto menu_id = menu_item.menu_id();
+    if (menu_id < 0)
+        return;
+
+    WindowServerConnection::the().async_flash_menubar_menu(m_window_id, menu_id);
+}
+
 bool Window::is_modified() const
 {
     if (!m_window_id)

Userland/Libraries/LibGUI/Window.h

@@ -211,6 +211,7 @@ public:
 
     Menu& add_menu(String name);
     ErrorOr<NonnullRefPtr<Menu>> try_add_menu(String name);
+    void flash_menubar_menu_for(const MenuItem&);
 
     void flush_pending_paints_immediately();
 

Userland/Libraries/LibGUI/WindowServerConnection.cpp

@@ -172,6 +172,7 @@ void WindowServerConnection::key_down(i32 window_id, u32 code_point, u32 key, u3
 
     if (auto* action = action_for_key_event(*window, *key_event)) {
         if (action->is_enabled()) {
+            action->flash_menubar_menu();
             action->activate();
             return;
         }