Adds OffHeapQuantizedFloatVectorValues to access float vectors when only quantized vectors are present (#14792)

Author: Pulkitg64

lucene/CHANGES.txt

@@ -32,6 +32,8 @@ New Features
 
 * GITHUB#14178: Add a Faiss-based vector format in the sandbox module. (Kaival Parikh)
 
+* GITHUB#14792: Introduced OffHeapQuantizedFloatVectorValues class to access float vectors when only quantized byte vectors are available in the index. (Pulkit Gupta)
+
 Improvements
 ---------------------
 

lucene/core/src/java/org/apache/lucene/codecs/lucene99/Lucene99ScalarQuantizedVectorsReader.java

@@ -189,6 +189,20 @@ private FieldEntry getFieldEntry(String field) {
   public FloatVectorValues getFloatVectorValues(String field) throws IOException {
     final FieldEntry fieldEntry = getFieldEntry(field);
     final FloatVectorValues rawVectorValues = rawVectorsReader.getFloatVectorValues(field);
+    if (rawVectorValues.size() == 0) {
+      return OffHeapQuantizedFloatVectorValues.load(
+          fieldEntry.ordToDoc,
+          fieldEntry.dimension,
+          fieldEntry.size,
+          fieldEntry.scalarQuantizer,
+          fieldEntry.similarityFunction,
+          vectorScorer,
+          fieldEntry.compress,
+          fieldEntry.vectorDataOffset,
+          fieldEntry.vectorDataLength,
+          quantizedVectorData);
+    }
+
     OffHeapQuantizedByteVectorValues quantizedByteVectorValues =
         OffHeapQuantizedByteVectorValues.load(
             fieldEntry.ordToDoc,