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/server/wire.go

@@ -9,6 +9,7 @@ import (
 	"github.com/grafana/grafana/pkg/api"
 	"github.com/grafana/grafana/pkg/api/routing"
 	"github.com/grafana/grafana/pkg/bus"
+	"github.com/grafana/grafana/pkg/expr"
 	"github.com/grafana/grafana/pkg/infra/httpclient"
 	"github.com/grafana/grafana/pkg/infra/httpclient/httpclientprovider"
 	"github.com/grafana/grafana/pkg/infra/kvstore"
@@ -57,7 +58,6 @@ import (
 	"github.com/grafana/grafana/pkg/services/sqlstore"
 	"github.com/grafana/grafana/pkg/services/updatechecker"
 	"github.com/grafana/grafana/pkg/setting"
-	"github.com/grafana/grafana/pkg/tsdb"
 	"github.com/grafana/grafana/pkg/tsdb/azuremonitor"
 	"github.com/grafana/grafana/pkg/tsdb/cloudmonitoring"
 	"github.com/grafana/grafana/pkg/tsdb/cloudwatch"
@@ -65,6 +65,8 @@ import (
 	"github.com/grafana/grafana/pkg/tsdb/grafanads"
 	"github.com/grafana/grafana/pkg/tsdb/graphite"
 	"github.com/grafana/grafana/pkg/tsdb/influxdb"
+	"github.com/grafana/grafana/pkg/tsdb/legacydata"
+	legacydataservice "github.com/grafana/grafana/pkg/tsdb/legacydata/service"
 	"github.com/grafana/grafana/pkg/tsdb/loki"
 	"github.com/grafana/grafana/pkg/tsdb/mssql"
 	"github.com/grafana/grafana/pkg/tsdb/mysql"
@@ -76,8 +78,8 @@ import (
 )
 
 var wireBasicSet = wire.NewSet(
-	tsdb.NewService,
-	wire.Bind(new(plugins.DataRequestHandler), new(*tsdb.Service)),
+	legacydataservice.ProvideService,
+	wire.Bind(new(legacydata.RequestHandler), new(*legacydataservice.Service)),
 	alerting.ProvideAlertEngine,
 	wire.Bind(new(alerting.UsageStatsQuerier), new(*alerting.AlertEngine)),
 	setting.NewCfgFromArgs,
@@ -164,6 +166,7 @@ var wireBasicSet = wire.NewSet(
 	datasources.ProvideService,
 	pluginsettings.ProvideService,
 	alerting.ProvideService,
+	expr.ProvideService,
 )
 
 var wireSet = wire.NewSet(