This one is a bit more involved. Of note is the fact that it at present
only uses local flow when determining the origin of some value (whereas
the points-to version used global flow). It may be desirable to rewrite
this query to use global data-flow, but this should be done with some
care (as using "all unhashable objects" as the set of sources is
somewhat iffy with respect to performance). For that reason, I'm
sticking to mostly local flow (except for well behaved things like types
and built-ins).
Moves the existing points-to predicates to the newly added class
`ControlFlowNodeWithPointsTo` which resides in the `LegacyPointsTo`
module.
(Existing code that uses these predicates should import this module, and
references to `ControlFlowNode` should be changed to
`ControlFlowNodeWithPointsTo`.)
Also updates all existing points-to based code to do just this.
