Stop creating lots of useless nodes in division / shape builder
Livarot doesn't coalesce segments that go through vertices with degree > 2. But these are exactly what we have after performing a cut operation. As a result, no coalescing would happen at all, leading to huge numbers of spurious nodes in both the cut operation and the shape builder (#471 (closed)).
This MR modifies livarot slightly, but in a safe way that just adds a flag that changes the coalescing behaviour, and this flag is only set to true in the case of cut operations.
If this is deemed backportable, and found to be without issues, I'll have to make a manual backport as this won't apply cleanly to 1.3.x.