elasticsearch Use the new FlatVectorsScorer

This commit removes the copy of the ScalarQuantizedVectorsWriter that we added in 8.14, in favour of a custom FlatVectorsScorer.

Previously we maintained the copy of the writer so that we could add a custom scorer implementation when merging scalar quantized vectors. This is not necessary now as we can provide a FlatVectorsScorer implementation that provides the custom scorer.

May 13 '24 16:05 ChrisHegarty

Pinging @elastic/es-search (Team:Search)

May 13 '24 16:05 elasticsearchmachine

@elasticmachine retest this please

May 13 '24 16:05 ChrisHegarty

https://github.com/apache/lucene/pull/13366

This fixes that tiny test vector failure.