feat: add voronoiDistanceTransform that propagates nearest labels (#107)

This generates both a "Voronoi"-like label map without gaps for an existing sparse label map (instead of points)
and the corresponding distance map to the original labels. 

fix: minor refactoring and modernization
feat: add shared createEuclideanDistance method


Co-authored-by: Stephan Saalfeld <[email protected]>

Author: bogovicj