Chore: Query endpoint refactor (#41637)

Get rid of using legacydata.RequestHandler in HTTPServer, /api/tsdb/query and pkg/expr 
with the goal of deprecating /api/tsdb/query and remove it completely eventually. This is 
the first step of cleaning up the HTTP API query endpoint.

Co-authored-by: Marcus Efraimsson <marcus.efraimsson@gmail.com>
Co-authored-by: Alexander Emelin <frvzmb@gmail.com>

pkg/tsdb/sqleng/sql_engine_test.go

@@ -1,7 +1,6 @@
 package sqleng
 
 import (
-	"database/sql"
 	"fmt"
 	"net"
 	"testing"
@@ -11,11 +10,9 @@ import (
 	"github.com/grafana/grafana-plugin-sdk-go/data"
 	"github.com/grafana/grafana-plugin-sdk-go/data/sqlutil"
 	"github.com/grafana/grafana/pkg/infra/log"
-	"github.com/grafana/grafana/pkg/tsdb/legacydata"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 	"github.com/xorcare/pointer"
-	"xorm.io/core"
 )
 
 func TestSQLEngine(t *testing.T) {
@@ -420,10 +417,6 @@ type testQueryResultTransformer struct {
 	transformQueryErrorWasCalled bool
 }
 
-func (t *testQueryResultTransformer) TransformQueryResult(columnTypes []*sql.ColumnType, rows *core.Rows) (legacydata.DataRowValues, error) {
-	return nil, nil
-}
-
 func (t *testQueryResultTransformer) TransformQueryError(err error) error {
 	t.transformQueryErrorWasCalled = true
 	return err