When reading JsonDocument and JsonElement, we currently first decode a string from our internal buffer, and parse that with JsonDocument.Parse() (see #2811). We could return a JsonDocument directly over the buffer (as a Memory), but would have to manage the buffer lifecycle - when we reread into the buffer, we would need to Dispose the JsonDocument instance we handed over to the user.

Not sure if CommandBehavior.SequentialAccess is enough of an explicit opt-in to this behavior - maybe it is.