Previously the method of picking the "target" duplicate wasn't
deterministic from a user perspective.
The behavior has been changed so:
- For a cluster of 3 or more vertices,
use the vertex closest to the centroid.
- For a cluster of 2 use the lowest index.
This mitigates #78916, solving some cases where clusters have a
central vertex although can't be considered fixed as the 2 vertex
case doesn't work so well.
Added a BLI_kdtree_{N}d_calc_duplicates_cb function that lets the
caller choose the index to keep from a cluster of duplicates.
Refactored from !145851.
Ref !146492
Co-authored-by: tariqsulley <tariqsulley3c@gmail.com>
bdae3e28a2