HPCC-12213 Add new WsDFU method to retrieve meta data

A new WsDFU method DFUGetFileMetaData is added to
retrieve MetaData from DFU IResultSetMetaData.

Signed-off-by: wangkx <kevin.wang@lexisnexis.com>
You could just have a local variable of the appropriate type:

DFUFileMetaDataReader dataReader(cursor->queryResultSet()->getMetaData());