Commands with a query component provide the ability to convert a PlanExecutor to a query planner BSON obj. These commands call an Explain::explainStages() override, which calls the Explain::generatePlannerInfo() to create the query planner.  The query planner contains a 'namespace' field that requires calling the namespace string serializer.  We will want to pass SerializationContext objects down the stack to correctly set the serialization configuration when serializing in generatePlannerInfo().

As the goal of these changes are in pursuit of fixing tests that will fail once serializeForCommands and deserializeForCommands are plumbed in, no new tests are being added for this ticket.