Complex types are not decoded if using many types

[Haeavar]

Describe the bug
If the complex types loading takes longer than creating the subscriptions, the complex types are not decoded (complex type system is not available in the binary decoder).

To Reproduce
Steps to reproduce the behavior:

1. Connect OpcPublisher to an aggregation OPC UA server with many types
2. Create a dataset with complex types
3. Observe that complex types are still binary encoded

Expected behavior
Complex types should be decoded

Additional context
Currently we have a bugfix on our own by adding an await GetComplexTypeSystemAsync in the OpcUaSubscription.SyncWithSessionInternalAsync. This is kind of a hack since the ISession does not provide such a method call (we need to cast it to OpcUaSession).
You might find a better place to fix this. You can give us a hint where is the best place to fix it and we can create a PR if you want.

image: mcr.microsoft.com/iotedge/opc-publisher:2.9.8

[marcschier]

Good catch, thanks. Fixed in #2279