Deprecate COSINE before Lucene 10 release

[benwtrent]

Description

Over a couple disparate discussions over various PRs/issues, we have tossed around the idea of deprecating COSINE.

To me, this makes sense, we shouldn't have COSINE at all IMO. Either users should normalize before indexing, or use max-inner product.

The question then becomes "What about byte vectors"? It seems to me that users should still use DOT_PRODUCT and MAX_INNER_PRODUCT.

[jmazanec15]

@benwtrent Is the main reason to deprecate to stop enabling users to setup non-optimal configurations? Or are there limitations cosine similarity imposes on implementation/optimization for other distance metrics?

[benwtrent]

@jmazanec15

Mainly because cosine has no benefit over normalizing & using dot_product and maintaining optimized Cosine similarity functions is an unnecessary burden for Lucene.

[jmazanec15]

Thanks @benwtrent that makes sense