Blender Git Loki

Cleanup: Use signed integers in the weld modifier

The style guide mentions that unsigned integers shouldn't be used to
show that a value won't be negative. Many places don't follow this
properly yet. The modifier used to cast an array of `uint` to `int` in
order to pass it to `BLI_kdtree_3d_calc_duplicates_fast`. That is no
longer necessary.

Differential Revision: https://developer.blender.org/D13613