In the updated tests, we used functions like disable_xform and
enable_xform to hint the optimizer to disallow/allow a particular
physical node. However, these functions are only available when GPDB
is built with GPORCA. Planner on the other hand accomplished this
via a GUC.

To avoid usage of these functions in tests, I have introduced couple
of GUCS that mimic the same planner behavior but now for GPORCA.
In this effort I needed to add an API inside GPORCA.