New Layouts: There 3 mode of a layout of the settings tabpanel :

1. Old mode, as it was always.
2. New mode, when Settings Tabs are hidden on the Plater. Use "cog" icon for the switching to the settings tabs
3. Dlg mode, when Settings Tabs are extracted to the Settings dialog. Use "cog" icon for Show or Focus the Settings Dialog

The "Collapse sidebar" toolbar appearance is set in the Preferences.

src/slic3r/GUI/Preferences.hpp

@@ -31,6 +31,7 @@ protected:
     void on_dpi_changed(const wxRect &suggested_rect) override;
     void layout();
     void create_icon_size_slider();
+    void create_settings_mode_widget();
 };
 
 } // GUI