Make the Query experimental

Author: dungba88

lucene/core/src/java/org/apache/lucene/search/TwoPhaseKnnVectorQuery.java

@@ -27,7 +27,11 @@
 import org.apache.lucene.util.ArrayUtil;
 import org.apache.lucene.util.Bits;
 
-/** A subclass of KnnFloatVectorQuery which does oversampling and full-precision reranking. */
+/**
+ * A subclass of KnnFloatVectorQuery which does oversampling and full-precision reranking.
+ *
+ * @lucene.experimental
+ */
 public class TwoPhaseKnnVectorQuery extends KnnFloatVectorQuery {
 
   private final int originalK;