HPCC-9355 Allow pasting of XGMML

Allow user to paste and edit raw XGMML.

Fixes HPCC-9355

Signed-off-by: Gordon Smith <gordon.smith@lexisnexis.com>
Merge pull request #4401 from GordonSmith/HPCC-9355

HPCC-9355 Allow pasting of XGMML

Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>