[HUDI-1196] Update HoodieKey when deduplicating records with global index (#2248)

- Works only for overwrite payload (default)
- Does not alter current semantics otherwise 

Co-authored-by: Ryan Pifer <ryanpife@amazon.com>

hudi-client/hudi-spark-client/src/main/java/org/apache/hudi/table/action/commit/SparkWriteHelper.java

@@ -59,10 +59,9 @@ public class SparkWriteHelper<T extends HoodieRecordPayload,R> extends AbstractW
     }).reduceByKey((rec1, rec2) -> {
       @SuppressWarnings("unchecked")
       T reducedData = (T) rec1.getData().preCombine(rec2.getData());
-      // we cannot allow the user to change the key or partitionPath, since that will affect
-      // everything
-      // so pick it from one of the records.
-      return new HoodieRecord<T>(rec1.getKey(), reducedData);
+      HoodieKey reducedKey = rec1.getData().equals(reducedData) ? rec1.getKey() : rec2.getKey();
+
+      return new HoodieRecord<T>(reducedKey, reducedData);
     }, parallelism).map(Tuple2::_2);
   }