LibCore+LibGUI+WindowServer: Make events bubble up through ancestors

With this patch, CEvents no longer stop at the target object, but will
bubble up the ancestor chain as long as CEvent::is_accepted() is false.

To the set accepted flag, call CEvent::accept().
To clear the accepted flag, call CEvent::ignore().

Events start out in the accepted state, so if you want them to bubble
up, you have to call ignore() on them.

Using this mechanism, we now ignore non-tabbing keydown events in
GWidget, causing them to bubble up through the widget's ancestors. :^)

Libraries/LibCore/CEvent.h

@@ -31,8 +31,13 @@ public:
 
     unsigned type() const { return m_type; }
 
+    bool is_accepted() const { return m_accepted; }
+    void accept() { m_accepted = true; }
+    void ignore() { m_accepted = false; }
+
 private:
     unsigned m_type { Type::Invalid };
+    bool m_accepted { true };
 };
 
 class CDeferredInvocationEvent : public CEvent {

Libraries/LibCore/CEventLoop.cpp

@@ -245,7 +245,7 @@ void CEventLoop::pump(WaitMode mode)
 #endif
             static_cast<CDeferredInvocationEvent&>(event).m_invokee(*receiver);
         } else {
-            receiver->event(event);
+            receiver->dispatch_event(event);
         }
 
         if (m_exit_requested) {

Libraries/LibCore/CObject.cpp

@@ -134,3 +134,24 @@ void CObject::save_to(JsonObject& json)
     json.set("name", name());
     json.set("parent", String::format("%p", parent()));
 }
+
+bool CObject::is_ancestor_of(const CObject& other) const
+{
+    if (&other == this)
+        return false;
+    for (auto* ancestor = other.parent(); ancestor; ancestor = ancestor->parent()) {
+        if (ancestor == this)
+            return true;
+    }
+    return false;
+}
+
+void CObject::dispatch_event(CEvent& e, CObject* stay_within)
+{
+    ASSERT(!stay_within || stay_within == this || stay_within->is_ancestor_of(*this));
+    auto* target = this;
+    do {
+        target->event(e);
+        target = target->parent();
+    } while (target && target != stay_within && !e.is_accepted());
+}

Libraries/LibCore/CObject.h

@@ -48,6 +48,8 @@ public:
     template<typename T, typename Callback>
     void for_each_child_of_type(Callback callback);
 
+    bool is_ancestor_of(const CObject&) const;
+
     CObject* parent() { return m_parent; }
     const CObject* parent() const { return m_parent; }
 
@@ -71,6 +73,8 @@ public:
 
     static IntrusiveList<CObject, &CObject::m_all_objects_list_node>& all_objects();
 
+    void dispatch_event(CEvent&, CObject* stay_within = nullptr);
+
 protected:
     explicit CObject(CObject* parent = nullptr, bool is_widget = false);