A definition of the group inside the list. A group can contain one or more list items (buttons).
items : Collection<ListDropdownButtonDefinition>
module:ui/dropdown/utils~ListDropdownGroupDefinition#items
The collection of the child list items inside this group.
label : string
module:ui/dropdown/utils~ListDropdownGroupDefinition#label
The visible label of the group.
type : 'group'
module:ui/dropdown/utils~ListDropdownGroupDefinition#type