Lucene99HnswVectorsReader[.readFields] readability tweaks (#13532)

* remove unnecessary readFields parameter
* consistently use this. in constructor
* align declare and init order

lucene/core/src/java/org/apache/lucene/codecs/lucene99/Lucene99HnswVectorsReader.java

@@ -68,10 +68,10 @@ public final class Lucene99HnswVectorsReader extends KnnVectorsReader
   private static final long SHALLOW_SIZE =
       RamUsageEstimator.shallowSizeOfInstance(Lucene99HnswVectorsFormat.class);
 
+  private final FlatVectorsReader flatVectorsReader;
   private final FieldInfos fieldInfos;
   private final Map<String, FieldEntry> fields = new HashMap<>();
   private final IndexInput vectorIndex;
-  private final FlatVectorsReader flatVectorsReader;
 
   public Lucene99HnswVectorsReader(SegmentReadState state, FlatVectorsReader flatVectorsReader)
       throws IOException {
@@ -93,13 +93,13 @@ public Lucene99HnswVectorsReader(SegmentReadState state, FlatVectorsReader flatV
                 Lucene99HnswVectorsFormat.VERSION_CURRENT,
                 state.segmentInfo.getId(),
                 state.segmentSuffix);
-        readFields(meta, state.fieldInfos);
+        readFields(meta);
       } catch (Throwable exception) {
         priorE = exception;
       } finally {
         CodecUtil.checkFooter(meta, priorE);
       }
-      vectorIndex =
+      this.vectorIndex =
           openDataInput(
               state,
               versionMeta,
@@ -154,9 +154,9 @@ private static IndexInput openDataInput(
     }
   }
 
-  private void readFields(ChecksumIndexInput meta, FieldInfos infos) throws IOException {
+  private void readFields(ChecksumIndexInput meta) throws IOException {
     for (int fieldNumber = meta.readInt(); fieldNumber != -1; fieldNumber = meta.readInt()) {
-      FieldInfo info = infos.fieldInfo(fieldNumber);
+      FieldInfo info = fieldInfos.fieldInfo(fieldNumber);
       if (info == null) {
         throw new CorruptIndexException("Invalid field number: " + fieldNumber, meta);
       }