Deep refactoring of ComputeStepAndHit

Both entering and exiting loops now relocate after each frame is found closer.

Added EnterCS method handling finding the closest entering frame and relocating after CS crossing. A frame hit can be provided to bootstrap the search for daughters only.

Child frames are now marked as embedded if this holds for any parent if there are more parent frames on the same side. By default, frames are marked as not embedded. Frames are sorted on the CS by the embedding property, not embedded first.