StreamWriter APIs loses information about leaf-set ordering

leaf-list noderefs {
ordered-by user;
type inv:node-connector-ref;
}

BindingStreamEventWriter and NormalizedNodeStreamWriter APIs looses information
about ordered-by statement of leaf-list by not exposing proper event, so underlying
implementations were free to choose more efficient unordered implementation (leaf-list
is set by definition).

This caused reordering of leaf-list entries.

Ordered-by statement works for list items. User ordered leaf-list are supported in Data Store and other pieces of infrastructure.