* Split ops into X_graph variants as discussed;
* Remove tokens from non-Graph region variants and rely on side-effect
modelling there while removing side-effect modelling from Graph
variants and relying on explicit ordering there;
* Make tokens required to be produced by Graph variants - but kept
explicit token type specification given previous discussion on this
potentially being configurable in future;
This results in duplicating some code. I considered adding helper
functions but decided against adding an abstraction there early given
size of duplication and creating accidental coupling.
Differential Revision: https://reviews.llvm.org/D127813
d30c0221cf