Resolve dependent SCs table.
Set up the __6MODEL_CORE__ SC.
Stub STables and objects at deserialization start.
Fill out STable and object deserialization logic.

This also adds the REPR deserialize functions for some representations
but others (especially the rather more complex P6opaque) are to come.
This gets a knowhow with a method in to deserialize well enough to be
able to call the method, at least.
Twiddle deserialization code-gen a little.