Introducing the MultiSelectListbox component

MultiSelectListbox is a selection component that can be used to select an item from a collection of items with the parent-child hierarchical relationship.

For example, in e-commerce applications, we can display various types of categories and associated subcategories using MultiSelectListbox.

For the MultiSelectListbox component, we need to give a list of SelectItem instances, where each item can be a SelectItemGroup instance with its associated child SelectItem instances.