Refactor codec to leverage backwards_codecs (#2546)

Refactors codec management to move codecs that are read only into a new
package, backwards codecs. Also, remove codecs that can no longer be
used in 3.0 (everything before 9.1.

With this, I remove the enum structure of KNNCodecVersion, as there is
really only one codec that can be used to actively write at a time.

Signed-off-by: John Mazanec <jmazane@amazon.com>

CHANGELOG.md

@@ -15,6 +15,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 ### Maintenance
 * Update package name to fix compilation issue [#2513](https://github.com/opensearch-project/k-NN/pull/2513)
 ### Refactoring
+* Refactor codec to leverage backwards_codecs [#2546](https://github.com/opensearch-project/k-NN/pull/2546)
 
 ## [Unreleased 2.x](https://github.com/opensearch-project/k-NN/compare/2.19...2.x)
 ### Features

src/main/java/org/opensearch/knn/index/codec/KNN10010Codec/KNN10010Codec.java

@@ -12,31 +12,37 @@
 import org.apache.lucene.codecs.FilterCodec;
 import org.apache.lucene.codecs.KnnVectorsFormat;
 import org.apache.lucene.codecs.StoredFieldsFormat;
+import org.apache.lucene.codecs.lucene101.Lucene101Codec;
 import org.apache.lucene.codecs.perfield.PerFieldKnnVectorsFormat;
 import org.opensearch.index.mapper.MapperService;
+import org.opensearch.knn.index.codec.KNN80Codec.KNN80CompoundFormat;
+import org.opensearch.knn.index.codec.KNN80Codec.KNN80DocValuesFormat;
 import org.opensearch.knn.index.codec.KNN9120Codec.DerivedSourceStoredFieldsFormat;
-import org.opensearch.knn.index.codec.KNNCodecVersion;
-import org.opensearch.knn.index.codec.KNNFormatFacade;
+import org.opensearch.knn.index.codec.KNN9120Codec.KNN9120PerFieldKnnVectorsFormat;
 import org.opensearch.knn.index.codec.derivedsource.DerivedSourceReadersSupplier;
 
+import java.util.Optional;
+
 /**
  * KNN Codec that wraps the Lucene Codec which is part of Lucene 10.0.1
  */
 
 public class KNN10010Codec extends FilterCodec {
 
-    private static final KNNCodecVersion VERSION = KNNCodecVersion.V_10_01_0;
-    private final KNNFormatFacade knnFormatFacade;
+    private static final String NAME = "KNN10010Codec";
+    public static final Codec DEFAULT_DELEGATE = new Lucene101Codec();
+    private static final PerFieldKnnVectorsFormat DEFAULT_KNN_VECTOR_FORMAT = new KNN9120PerFieldKnnVectorsFormat(Optional.empty());
+
     private final PerFieldKnnVectorsFormat perFieldKnnVectorsFormat;
     private final StoredFieldsFormat storedFieldsFormat;
 
     private final MapperService mapperService;
 
     /**
-     * No arg constructor that uses Lucene99 as the delegate
+     * No arg constructor that uses Lucene101Codec as the delegate
      */
     public KNN10010Codec() {
-        this(VERSION.getDefaultCodecDelegate(), VERSION.getPerFieldKnnVectorsFormat(), null);
+        this(DEFAULT_DELEGATE, DEFAULT_KNN_VECTOR_FORMAT, null);
     }
 
     /**
@@ -47,22 +53,21 @@ public KNN10010Codec() {
      * @param knnVectorsFormat per field format for KnnVector
      */
     @Builder
-    protected KNN10010Codec(Codec delegate, PerFieldKnnVectorsFormat knnVectorsFormat, MapperService mapperService) {
-        super(VERSION.getCodecName(), delegate);
-        knnFormatFacade = VERSION.getKnnFormatFacadeSupplier().apply(delegate);
+    public KNN10010Codec(Codec delegate, PerFieldKnnVectorsFormat knnVectorsFormat, MapperService mapperService) {
+        super(NAME, delegate);
         perFieldKnnVectorsFormat = knnVectorsFormat;
         this.mapperService = mapperService;
         this.storedFieldsFormat = getStoredFieldsFormat();
     }
 
     @Override
     public DocValuesFormat docValuesFormat() {
-        return knnFormatFacade.docValuesFormat();
+        return new KNN80DocValuesFormat(delegate.docValuesFormat());
     }
 
     @Override
     public CompoundFormat compoundFormat() {
-        return knnFormatFacade.compoundFormat();
+        return new KNN80CompoundFormat(delegate.compoundFormat());
     }
 
     @Override