s4-dsdb/schema: Implement multi-pass working schema creation function

s4-dsdb/schema: Implement multi-pass working schema creation function

It is heavily based on implementation in libnet_vampire_cb_apply_schema()
function, except that it actually creates a new copy of the supplied
initial_schema + resolving all incoming objects and add them to
supplied initial_schema.

We are going to need this 'working_schema' later so we are able
to fully resolve all objects we receive on wire during DRS replication.

Working schema created is to be used only as an index to search in.
It is not supposed to be set to an ldb_context as it doesn't
contain all information for classSchema and attributeSchema objects.