New Excel APIs: Workbook.getSelectedRangeOrNullObject and Workbook.getSelectedRangesOrNullObject.

There are currently only the APIs Workbook.getSelectedRange and Workbook.getSelectedRanges. In case of errors, we need to catch the exception. Like for other APIs, the respective Workbook.getSelectedRangeOrNullObject and Workbook.getSelectedRangesOrNullObject APIs would help to control errors better.