HPCC-9335 Track end of file from inputs used in stepped join

Signed-off-by: Gavin Halliday <gavin.halliday@lexisnexis.com>
HPCC-9335 Improvements to single stepping nested merge joins

Signed-off-by: Gavin Halliday <gavin.halliday@lexisnexis.com>
HPCC-9335 Fix potential core if the input doesn't support stepping

Signed-off-by: Gavin Halliday <gavin.halliday@lexisnexis.com>
HPCC-9335 Add some GRAPH based stepping tests

Signed-off-by: Gavin Halliday <gavin.halliday@lexisnexis.com>
HPCC-9335 Smart stepping join continues to request rows after end of file

Pass information about whether the passed in seeks represent the final set of
desired matches to the slave node.

Stepping information not being returned from single graph result.

Added/tweaked tracing.

Signed-off-by: Richard Chapman <rchapman@hpccsystems.com>
Merge pull request #4396 from richardkchapman/rkcissue9335

Global Smart Stepping fixes

Reviewed-By: Jake Smith <jake.smith@lexisnexis.com>
Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>