Support grouping of vector data in HNSW

[heemin32]

Add IDGrouper in SearchParameter so that it can be used to dedupe search result based on its group id.

Issue: #3087

[heemin32]

@mdouze , would you mind taking a look?

[mdouze]

Sorry for being unresponsive.
The reason I'm reluctant with this solution is that IMO the new ResultHandler API makes it possible to move the whole de-duplication logic outside of Faiss. In the calling code, just set up a ResultHandler class that does the deduplication and call hnsw.search on that.

[heemin32]

I search HNSW through IndexIDMap. Do you have a plan to expand the ResultHandler to IndexIDMap? I need a way to access id_map data to dedupe result properly.

[mdouze]

I still have to write an example with a custom ResultHandler.