The IAccessible NVDAObject currently uses IAccessibleTable to fetch row/column counts/indexes and IAccessibleTableCell for row/column headers. However, QT5 only supports IAccessibleTable2/Cell, not the older IAccessibleTable. It's reasonable to assume future implementations might do the same, though we still need to support IAccessibleTable for older implementations such as Symphony/OpenOffice/LibreOffice.

This will require additions to the table, tableID, rowCount, columnCount, rowNumber and columnNumber properties to use the new interfaces if they are available.

Note that we have an existing _IATableCell property to get that interface.