Struct JobMergeNearbyVertices Extends IJob

Removes duplicate vertices from the array and updates the triangle array.

Uses a sweep line algorithm. For mergeRadiusSq=0, this is slower than a hash map based approach (by a factor of 3-4 even, primarily due to the sort), but this code doesn't tend to be a bottleneck so it's not a big deal. A hash based approach cannot easily support a mergeRadiusSq > 0.

A hash based approach was removed in the commit after cc57efb0c.