[RotateForLoops] Add unit tests to loop rotation pass

[lucas-rami]

A recent commit (aa8eca2) improved the for loop rotation pass to let it handle loops with negative bounds. This generalization makes at least one of our standard benchmark (sobel) yield a better circuit because two additional loops of the original source code are able to be matched and converted by our pass.

The pass currently lacks some unit tests, which is obviously not ideal. We should add some and, at the same time, take the opportunity to rename the TableGen-defined pass to ScfRotateForLoops (replacing ScfForLoopRotation) to follow standard pass naming conventions.