getDataList
Retrieves a list of AppInfoData objects based on the specified item type.
This is an abstract function that must be implemented by concrete subclasses to provide the actual data retrieval logic.
Return
A list of AppInfoData objects corresponding to the given item type. Returns an empty list if no data is found or if the item type is not supported.
Parameters
itemType
An integer representing the type of items to retrieve. For example, TYPE_ITEM_TEXT.