The node outputs the index of the closest element to itself. See #102387
for the original design.
This is different from the Sample Nearest node in two important ways:
* It does not have a geometry input, instead the geometry is taken from the
field evaluation context.
* The node can exclude the "current" element from the search.
* The group id input can be used to build subsets of elements that only
consider each other as neighbors and ignore elements with other ids.
Pull Request: https://projects.blender.org/blender/blender/pulls/104619
15f9e42c4f