Merge cockroachdb#39364

39364: opt: turn optimizer on in schema changer r=RaduBerinde a=RaduBerinde

The schema changer sets up a custom `SessionData`; it wasn't
initializing the `OptimizerMode` field. This change sets it to On
(which is normally the default).

Release note: None

Co-authored-by: Radu Berinde <radu@cockroachlabs.com>

pkg/sql/schema_changer.go

@@ -2269,7 +2269,8 @@ func createSchemaChangeEvalCtx(
 		DataConversion: sessiondata.DataConversionConfig{
 			Location: dummyLocation,
 		},
-		User: security.NodeUser,
+		User:          security.NodeUser,
+		OptimizerMode: sessiondata.OptimizerOn,
 	}
 
 	evalCtx := extendedEvalContext{