A module has both a Java and a C++ representation

    C++: ModuleEntry
    Java: java.lang.Module

In C++, we have the following two methods

    ModuleEntry* InstanceKlass::module()
    oop ModuleEntry::module();

This can lead to confusing code like this:

    InstanceKlass* ik = ...;
    oop module = ik->module()->module()

Proposal:

- Leave InstanceKlass::module() as is -- there's another function with the same style: "PackageEntry* InstanceKlass::package()"
- Rename ModuleEntry::module() to ModuleEntry::module_oop(), so the above example can be more readable:

    InstanceKlass* ik = ...;
    oop module = ik->module()->module_oop()