Fix #117515: Geometry Nodes: Count of unique face neighbors
Regular topology mapping does not care about deduplication of relations. And
this is correct for a lot of the case where we expect creating difference of this
relations in next operations. But this is not the case for users, since this should
be actually trivial info. Due to this reason, construct full topology map and count
number of unique connections. Performance side: difference linear check and
hash set for different sizes of connections set.
Pull Request: https://projects.blender.org/blender/blender/pulls/118848