MMU segmentation no longer works directly on lslices, instead of it works on custom merged regions. So lslices in PrintObject are no longer overwritten because of MMU segmentation.
All regions are scaled by SCALED_EPSILON before merging and shrunk back by SCALED_EPSILON after merging. That fixed issues with multi-volume objects when very close regions weren't merged.
Also, small expolygons and holes are filtered out that fixed missing segmentation at the boundary of two volumes in the case of multi-volume objects.
Serialization and deserialization in TriangleSelector were extended to support up to 16 materials (3 unused states left for possible later extension). These changes also affect the encoding of data from custom supports and seams, but it is backward compatible with the previous encoding. And for custom supports and seams, it is produced exactly the same data encoding as before.
the code more readable and to highlight where PrintObject::region_volumes
are actually set and consumed.
2) Replaced Slic3r::clamp() with std::clamp(). They differ in the order
of their parameters, thus hopefully no new bugs were introduced.
3) Some refactoring of MultiMaterialSegmentation for efficiency.
