Chore: Refactor usage of legacy data contracts (#41218)

Refactor usage of legacy data contracts. Moves legacy data contracts 
to pkg/tsdb/legacydata package.
Refactor pkg/expr to be a proper service/dependency that can be provided 
to wire to remove some unneeded dependencies to SSE in ngalert and other places.
Refactor pkg/expr to not use the legacydata,RequestHandler and use 
backend.QueryDataHandler instead.

pkg/tsdb/testdatasource/scenarios_test.go

@@ -9,7 +9,7 @@ import (
 	"github.com/grafana/grafana-plugin-sdk-go/backend"
 	"github.com/grafana/grafana-plugin-sdk-go/data"
 	"github.com/grafana/grafana/pkg/components/simplejson"
-	"github.com/grafana/grafana/pkg/plugins"
+	"github.com/grafana/grafana/pkg/tsdb/legacydata"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 )
@@ -19,7 +19,7 @@ func TestTestdataScenarios(t *testing.T) {
 
 	t.Run("random walk ", func(t *testing.T) {
 		t.Run("Should start at the requested value", func(t *testing.T) {
-			timeRange := plugins.DataTimeRange{From: "5m", To: "now", Now: time.Now()}
+			timeRange := legacydata.DataTimeRange{From: "5m", To: "now", Now: time.Now()}
 
 			model := simplejson.New()
 			model.Set("startValue", 1.234)
@@ -63,7 +63,7 @@ func TestTestdataScenarios(t *testing.T) {
 
 	t.Run("random walk table", func(t *testing.T) {
 		t.Run("Should return a table that looks like value/min/max", func(t *testing.T) {
-			timeRange := plugins.DataTimeRange{From: "5m", To: "now", Now: time.Now()}
+			timeRange := legacydata.DataTimeRange{From: "5m", To: "now", Now: time.Now()}
 
 			model := simplejson.New()
 			modelBytes, err := model.MarshalJSON()
@@ -117,7 +117,7 @@ func TestTestdataScenarios(t *testing.T) {
 		})
 
 		t.Run("Should return a table with some nil values", func(t *testing.T) {
-			timeRange := plugins.DataTimeRange{From: "5m", To: "now", Now: time.Now()}
+			timeRange := legacydata.DataTimeRange{From: "5m", To: "now", Now: time.Now()}
 
 			model := simplejson.New()
 			model.Set("withNil", true)