1) Make unroll code reusable 2) reduce non-determinisim in CanonicalSimplify (#701)

* 1) Refactored some parts of the unrolling code into their own methods so we can reuse unrolling functionality in other parts of the code. E.g., to explicitly unroll loops with count of 1 when they are programmatically created.
2) Reorder based on top operator before resorting to pointers, which causes non-determinism.

* Fixed lint errors