This frees `Class.qll`, `Exprs.qll`, and `Function.qll` from the
clutches of points-to. For the somewhat complicated setup with
`getLiteralObject` (an abstract method), I opted for a slightly ugly but
workable solution of just defining a predicate on `ImmutableLiteral`
that inlines each predicate body, special-cased to the specific instance
to which it applies.
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.
