Support Teradata Query Folding of Date and DateTime Arithmetic

[markew1]

For example, #"Added Custom" = Table.AddColumn ( #"Removed Other Columns", "Custom", each Duration.Days ( [ROW_MODIFY_GMT_DTTM] - [ROW_CREATE_GMT_DTTM] )) ... should query fold. In Teradata subtraction of 2 dates produces the days between the 2 dates.