Ghost cells generator: kdtree point locator

In the unstructured data subroutine, a vtkStaticPointLocator was used to match interfacing points with points sent by neighbors. In the instance of unstructured grids with a lot of discrepencies in point density over the data set, this point locator could become extremely slow. This is because the static point locator uses cubic buckets and brute-force search inside the bucket in which the query point is. In the instance of querying in a bucket with high resolution data, the search is very slow.

To speed up the filter for this case scenario, vtkStaticPointLocator is replaced by vtkKdTreePointLocator.

Addresses paraview/paraview#20926 (closed)