Use jstream to serialize records to JSON format in S3Select (#7318)

- Also, switch to jstream to generate internal record representation
  from CSV/JSON readers

- This fixes a bug in which JSON output objects have their keys
  reversed from the order they are specified in the Select columns.

- Also includes a fix for tests.

pkg/s3select/csv/record.go

@@ -19,10 +19,11 @@ package csv
 import (
 	"bytes"
 	"encoding/csv"
+	"encoding/json"
 	"fmt"
 
+	"github.com/bcicen/jstream"
 	"github.com/minio/minio/pkg/s3select/sql"
-	"github.com/tidwall/sjson"
 )
 
 // Record - is CSV record.
@@ -78,20 +79,11 @@ func (r *Record) MarshalCSV(fieldDelimiter rune) ([]byte, error) {
 
 // MarshalJSON - encodes to JSON data.
 func (r *Record) MarshalJSON() ([]byte, error) {
-	data := "{}"
-
-	var err error
-	for i := len(r.columnNames) - 1; i >= 0; i-- {
-		if i >= len(r.csvRecord) {
-			continue
-		}
-
-		if data, err = sjson.Set(data, r.columnNames[i], r.csvRecord[i]); err != nil {
-			return nil, err
-		}
+	var kvs jstream.KVS = make([]jstream.KV, len(r.columnNames))
+	for i := 0; i < len(r.columnNames); i++ {
+		kvs[i] = jstream.KV{Key: r.columnNames[i], Value: r.csvRecord[i]}
 	}
-
-	return []byte(data), nil
+	return json.Marshal(kvs)
 }
 
 // NewRecord - creates new CSV record.