.Net: Fixed sorting for negative DOT product

[yorek]

Motivation and Context

When using negative dot product scoring, the more negative the value, the closer the vector is to the query vector.

Description

Fixed the sorting used for negative dot product distance calculations

Contribution Checklist

• The code builds clean without any errors or warnings
• The PR follows the SK Contribution Guidelines and the pre-submission formatting script raises no violations
• All unit tests pass, and I have added new tests where possible
• I didn't break anyone 😄

[westey-m]

Hi @yorek, thanks for the contribution, it makes sense. Do you mind also updating the integration test? It is also incorrect.
See VectorSearchDistanceFunctionComplianceTests.NegativeDotProductSimilarity, which is has an expectation defined that results are returned with least similar first, but should be most similar first, i.e. Same, Orthogonal, Opposite, instead of Opposite, Orthogonal, Same.

It looks like the only other DB that uses this test is Weaviate, which has been overridden to correctly test the order.

// Incorrect order:
this.SimpleSearch(DistanceFunction.NegativeDotProductSimilarity, -1, 1, 0, [1, 2, 0]);

// Correct order:
this.SimpleSearch(DistanceFunction.NegativeDotProductSimilarity, -1, 1, 0, [0, 2, 1]);

[yorek]

Thanks everyone for the quick turnaround!