[JIT] Freeze unrolls constant loops (#63614)

[JIT] Freeze unrolls constant loops (#63614)

Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/63614

There are a number of optimizations (`RemoveListMutation` in particular) that are tied to loop unrolling in `runOptimizations`. However, these were not invoked from `freeze_module` since the freezing pass should be idempotent.

This diff makes `runOptimizations` run `UnrollConstantLoops` instead of `UnrollLoops`. `freeze_module` is then able to run these optimizations.

Test Plan: Observed that `freeze_module` applies `RemoveListMutation`

Reviewed By: eellison

Differential Revision: D30437356

fbshipit-source-id: cba04bd958a48ad51b151aa3264f3d5bbb1fc2a4