LibGUI: Add a callback when the visible columns of a TableView change

Userland/Libraries/LibGUI/AbstractTableView.cpp

@@ -376,6 +376,9 @@ void AbstractTableView::header_did_change_section_visibility(Badge<HeaderView>,
 {
     update_content_size();
     update();
+
+    if (on_visible_columns_changed)
+        on_visible_columns_changed();
 }
 
 void AbstractTableView::set_default_column_width(int column, int width)

Userland/Libraries/LibGUI/AbstractTableView.h

@@ -44,6 +44,7 @@ public:
     // These return/accept a comma-separated list of column ids, for storing in a config file.
     ErrorOr<String> get_visible_columns() const;
     void set_visible_columns(StringView column_ids);
+    Function<void()> on_visible_columns_changed;
 
     int column_width(int column) const;
     void set_column_width(int column, int width);