Added SparamInitTest
IllegalConfigTest: add circular dependency test
Helper: add code mapping helpers

- mapping does more aggressive inference. It automatically uses the
  nested method for inferring constructor arguments from the nested
  parameters. This inference would be inappropriate in MappingCfg, so
  this method saves an extra builder call.
- codeMapping creates a complete CodeMappingCfg from only a ParamCfg
  and a Class object.
Added NestedDependencyTest
NestedDependencyTest: initial overshadowing test

This is test turns out to be a mere preview. More tests have to
be added.