LibGUI: Add option to move Toolbar items to overflow menu in groups

When items are sent to the overflow menu one by one, it can happen that
buttons that are heavily related, and don't make sense without one
another (either visually or logically) are separated.
This new option enables the developer to choose the "grouping"
behavior, of sending all items that are not separated to the overflow
menu together, as soon as one of them doesn't have enough space to be
displayed. (provided the toolbar is set as collapsible)

Userland/Libraries/LibGUI/Toolbar.cpp

@@ -27,6 +27,7 @@ Toolbar::Toolbar(Orientation orientation, int button_size)
     , m_button_size(button_size)
 {
     REGISTER_BOOL_PROPERTY("collapsible", is_collapsible, set_collapsible);
+    REGISTER_BOOL_PROPERTY("grouped", is_grouped, set_grouped);
 
     if (m_orientation == Orientation::Horizontal)
         set_fixed_height(button_size);
@@ -202,6 +203,16 @@ ErrorOr<void> Toolbar::update_overflow_menu()
         return {};
     }
 
+    if (m_grouped) {
+        for (size_t i = marginal_index.value(); i > 0; --i) {
+            auto& item = m_items.at(i);
+            if (item.type == Item::Type::Separator)
+                break;
+            item.widget->set_visible(false);
+            marginal_index = i;
+        }
+    }
+
     if (!m_overflow_action)
         TRY(create_overflow_objects());
     m_overflow_action->set_enabled(true);

Userland/Libraries/LibGUI/Toolbar.h

@@ -27,6 +27,8 @@ public:
 
     bool is_collapsible() const { return m_collapsible; }
     void set_collapsible(bool b) { m_collapsible = b; }
+    bool is_grouped() const { return m_grouped; }
+    void set_grouped(bool b) { m_grouped = b; }
 
     virtual Optional<UISize> calculated_preferred_size() const override;
     virtual Optional<UISize> calculated_min_size() const override;
@@ -58,6 +60,7 @@ private:
     const Gfx::Orientation m_orientation;
     int m_button_size { 24 };
     bool m_collapsible { false };
+    bool m_grouped { false };
 };
 
 }