Revisit the visibility check in type_resolve

[jjcnn]

The function resolve_call_path in type_resolve.rs in some cases performs a visibility check of the path being resolved. However, the visibility check is insufficient, because the prefixes of the path are only checked for visibility if the prefix refers to a module.

For example, for the path MyPackage::MyModule::MySubmodule::MyEnum::MyEnumVariant we do not check the visibility of MyEnum, since this identifier refers to an enum rather than to a module.

Note that accessing a private item is legal if the access is performed through a reexport, so it is not entirely trivial to solve this problem.