Improve position information for CIF invariants
From the output of !582:
```
WARNING: --------------------------------------------------------
WARNING: (2/2) Requirement invariant will be explored as a plant.
WARNING: --------------------------------------------------------
WARNING: * In the top-level scope of the specification:
WARNING: - requirement invariant r1.x + r2.x >= 0;
WARNING: ^
WARNING: * In automaton "r1":
WARNING: - requirement invariant x >= 0;
WARNING: ^
WARNING: - requirement invariant x >= 0;
WARNING: ^
WARNING: * In automaton "r2":
WARNING: - requirement invariant x >= 0;
WARNING: ^
WARNING: * In location "r2.loc":
WARNING: - requirement invariant x >= 0;
WARNING: ^
WARNING: - requirement invariant x <= 1 div x;
WARNING: ^
```
The position information for invariants should not be on the predicate, but on one of the keywords.
issue