private RelDataType getFieldType(RelNode relNode, int i) {
    final RelDataTypeField inputField =
        relNode.getRowType().getFieldList().get(i);
    return inputField.getType();
  }
Do a shallow clone of oldAggRel and update aggCalls. Could be refactored
into Aggregate and subclasses - but it's only needed for some
subclasses.

@param relBuilder Builder of relational expressions; at the top of its
                  stack is its input
@param oldAggregate LogicalAggregate to clone.
@param newCalls  New list of AggregateCalls
ql/src/java/org/apache/hadoop/hive/ql/optimizer/calcite/rules/HiveAggregateReduceFunctionsRule.java