Adds an item in a specified location.
function AddItem(Item: TListItem; Index: Integer = -1): TListItem;
__fastcall TListItem AddItem(TListItem Item, int Index = -1);
Call AddItem to add an Item at any place in the list. The properties of Item are duplicated if Item is not nil. Index is location of the added item; if Index is negative, the TListItem is appended to the end of the list.
AddItem returns the TListItem that was added.