Adjusts Seeded knn searches to clean up user and internal interfaces

[benwtrent]

This is a bugfix and refactor for seeded knn searches.

First, Since we are using collectors, we don't actually need unique queries for every input type. Consequently, I have collapsed the two individual seeded queries into a single query that delegates to a provided kNN query. Then the collector manager is simply wrapped, so that the entry points can be provided.

Second, the interactions in the hnsw graph were not clear. Consequently, I did a minor refactor of HNSW searcher to have a "SeededSearcher", where instead of searching the graph for the entry points, it provides them directly.

Third, since ordinal translating collector is wrapping the final collector provided, I made it an entry point provider. A separate option here is to remove this "entry point provider" interface altogether and add default methods to the base KnnCollector, which defaults to 0 entrypoints and empty iterator. Which means that we search the graph for the entry points.