XRes works in an odd way, the evaluation is inside the processui model,
then it gets sent back into the process and proxied round.
It leaves code in ProcessCore that doesn't work in a way one would expect.
Though for API compat it can't be completely tidied up yet.
By moving to a plugin we get no more ifdefs, no more special casing
inside the core model.
XRes extraction code is unchanged only moved