Add a new set of functions to allow ZObject argument types to be spliced.
Bug: T393130
The workflow is now
- convert everything except arguments to the request format;
- minimize types (maximal version was needed for type converter extraction);
- convert the type-minimized ZObjects for Avro;
- serialize with Avro.
It's a bit awkward, but the mess will be isolated to single orchestrator-side function.