Before this fix, graph preparation sometimes left extra long-edges not
connected to anything in. They were not visible after the SVG
exportation, but they were making edge routing worse (by forcing
horizontal lanes to appear where they shouldn't be - thus spacing nodes
further away from each other than necessary).
Since the `orderEdges` function no longer consumes the graph, we can
finally make the restoration step separate - leading to more explicitly
stated boundaries as to where the graph is a DAG, and where it is not.
Also removed a few entities to avoid duplication in the full names:
- `yield::layout::sugiyama::LayoutOrientation`
-> `yield::layout::sugiyama::Orientation`
- `yield::layout::sugiyama::layout(...)`
-> `yield::layout::sugiyama::compute(...)`
Giacomo Vercesi