LibWebView+UI: Add structures to hold context menu and action data

We currently duplicate a lot of code to handle application/context menus
and actions. The goal here is to hold the data for the menus and actions
in LibWebView. Each UI will then be able to generate menus from the data
on-the-fly.

The structures added here are meant to support generic and checkable
actions, action groups, submenus, etc.

Libraries/LibWebView/Menu.cpp

@@ -0,0 +1,126 @@
+/*
+ * Copyright (c) 2025, Tim Flynn <trflynn89@ladybird.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibWebView/Menu.h>
+
+namespace WebView {
+
+NonnullRefPtr<Action> Action::create(Variant<StringView, String> text, ActionID id, Function<void()> action)
+{
+    return adopt_ref(*new Action { move(text), id, move(action) });
+}
+
+NonnullRefPtr<Action> Action::create_checkable(Variant<StringView, String> text, ActionID id, Function<void()> action)
+{
+    auto checkable = create(move(text), id, move(action));
+    checkable->m_checked = false;
+    return checkable;
+}
+
+void Action::set_text(Variant<StringView, String> text)
+{
+    if (text.visit([&](auto const& text) { return text == this->text(); }))
+        return;
+    m_text = move(text);
+
+    for (auto& observer : m_observers)
+        observer->on_text_changed(*this);
+}
+
+void Action::set_tooltip(StringView tooltip)
+{
+    if (m_tooltip == tooltip)
+        return;
+    m_tooltip = tooltip;
+
+    for (auto& observer : m_observers)
+        observer->on_tooltip_changed(*this);
+}
+
+void Action::set_enabled(bool enabled)
+{
+    if (m_enabled == enabled)
+        return;
+    m_enabled = enabled;
+
+    for (auto& observer : m_observers)
+        observer->on_enabled_state_changed(*this);
+}
+
+void Action::set_visible(bool visible)
+{
+    if (m_visible == visible)
+        return;
+    m_visible = visible;
+
+    for (auto& observer : m_observers)
+        observer->on_visible_state_changed(*this);
+}
+
+void Action::set_checked(bool checked)
+{
+    set_checked_internal(checked);
+
+    if (auto group = m_group.strong_ref()) {
+        group->for_each_action([&](Action& action) {
+            if (action.is_checkable() && &action != this)
+                action.set_checked_internal(false);
+        });
+    }
+}
+
+void Action::set_checked_internal(bool checked)
+{
+    VERIFY(is_checkable());
+
+    if (m_checked == checked)
+        return;
+    m_checked = checked;
+
+    for (auto& observer : m_observers)
+        observer->on_checked_state_changed(*this);
+}
+
+void Action::add_observer(NonnullOwnPtr<Observer> observer)
+{
+    observer->on_text_changed(*this);
+    if (m_tooltip.has_value())
+        observer->on_tooltip_changed(*this);
+    observer->on_enabled_state_changed(*this);
+    observer->on_visible_state_changed(*this);
+    if (is_checkable())
+        observer->on_checked_state_changed(*this);
+
+    m_observers.append(move(observer));
+}
+
+void Action::remove_observer(Observer const& observer)
+{
+    m_observers.remove_first_matching([&](auto const& candidate) {
+        return candidate.ptr() == &observer;
+    });
+}
+
+NonnullRefPtr<Menu> Menu::create(StringView name)
+{
+    return adopt_ref(*new Menu { name });
+}
+
+NonnullRefPtr<Menu> Menu::create_group(StringView name)
+{
+    auto menu = create(name);
+    menu->m_is_group = true;
+    return menu;
+}
+
+void Menu::add_action(NonnullRefPtr<Action> action)
+{
+    if (m_is_group)
+        action->set_group({}, *this);
+    m_items.append(move(action));
+}
+
+}