slicedOptionGroup method
Creates a new option group with options from start
inclusive to end
exclusive, other properties stay the same.
Implementation
OptionGroup<T> slicedOptionGroup(int start, int end) {
List<T> subListItems = this.sublist(start, end);
return OptionGroup.withLabelFunction(
subListItems, hasLabel ? null : () => uiDisplayName, _emptyLabelFcn);
}