Init slice debug names in CodegenBinding
Generate Obj-C metaclasses to ...$metaclass

In order to do that, we now need to save FQN for these classes in objc-java
codegen, and then reuse the whole BindingContext in the usual codegen, along
with bindings from AnalyzeExhaust. The new ChainedBindingContext does just
that: it combines several binding contexts into one