Delegate xorBitCount to Lucene (#114249)

Now that we're on Lucene 9.12 we don't need our own optimized xorBitCount, can just delegate to Lucene's optimized one (which is identical).

Author: ChrisHegarty

server/src/main/java/org/elasticsearch/index/codec/vectors/ES815BitFlatVectorsFormat.java

@@ -17,11 +17,11 @@
 import org.apache.lucene.index.SegmentReadState;
 import org.apache.lucene.index.SegmentWriteState;
 import org.apache.lucene.index.VectorSimilarityFunction;
+import org.apache.lucene.util.VectorUtil;
 import org.apache.lucene.util.hnsw.RandomAccessVectorValues;
 import org.apache.lucene.util.hnsw.RandomVectorScorer;
 import org.apache.lucene.util.hnsw.RandomVectorScorerSupplier;
 import org.apache.lucene.util.quantization.RandomAccessQuantizedByteVectorValues;
-import org.elasticsearch.script.field.vectors.ESVectorUtil;
 
 import java.io.IOException;
 
@@ -105,7 +105,7 @@ public RandomVectorScorer getRandomVectorScorer(
     }
 
     static float hammingScore(byte[] a, byte[] b) {
-        return ((a.length * Byte.SIZE) - ESVectorUtil.xorBitCount(a, b)) / (float) (a.length * Byte.SIZE);
+        return ((a.length * Byte.SIZE) - VectorUtil.xorBitCount(a, b)) / (float) (a.length * Byte.SIZE);
     }
 
     static class HammingVectorScorer extends RandomVectorScorer.AbstractRandomVectorScorer {

server/src/main/java/org/elasticsearch/script/field/vectors/ByteBinaryDenseVector.java

@@ -103,7 +103,7 @@ public double l1Norm(List<Number> queryVector) {
 
     @Override
     public int hamming(byte[] queryVector) {
-        return ESVectorUtil.xorBitCount(queryVector, vectorValue);
+        return VectorUtil.xorBitCount(queryVector, vectorValue);
     }
 
     @Override

server/src/main/java/org/elasticsearch/script/field/vectors/ByteKnnDenseVector.java

@@ -104,7 +104,7 @@ public double l1Norm(List<Number> queryVector) {
 
     @Override
     public int hamming(byte[] queryVector) {
-        return ESVectorUtil.xorBitCount(queryVector, docVector);
+        return VectorUtil.xorBitCount(queryVector, docVector);
     }
 
     @Override