A decl’s full GenericSignature is set during validateGenericTypeSignature().
Then during ConstraintSystem::openTypes(), in ReplaceDependentTypes, the GenericArgs list is built from the generic signature (via getGenericParamTypes()) and passed into a new BoundGenericType.
In BoundGenericType::getSubstitutions(), the GenericArgs are assumed to match getGenericParamsOfContext()->getParams().
However, in reality, the GenericArgs include all levels of generic args, whereas getGenericParamsOfContext() are the params of the innermost context only, so the params array is accessed past its end.
This commit changes NominalTypeDecl::getGenericParamTypes() to return the innermost params, in order to match the output of BoundGenericType::getGenericArgs(). For clarity and to hopefully prevent future confusion, we also rename getGenericParamTypes() to getInnermostGenericParamTypes().
