Fix selection after inserting items in wxListBox in wxOSX

We need to adjust the indices of the currently selected items as we need
to keep the same items, not the same indices, selected after new items
insertion.

Closes #18902.

include/wx/osx/listbox.h

@@ -170,6 +170,8 @@ protected:
     wxArrayPtrVoid m_itemsClientData;
 
 private:
+    // Mostly the same as DoSetSelection() but doesn't call EnsureVisible().
+    void DoSetSelectionWithoutEnsureVisible(int n, bool select);
 
     wxDECLARE_DYNAMIC_CLASS(wxListBox);
     wxDECLARE_EVENT_TABLE();