Polymorphic inheritance for classes with the same name in different namespaces

[ajor]

It currently doesn't work due to the dependence on unqualified type names in resolving drgn types.

e.g. this setup:

namespace nsA {
  class MyClass {
  public:
    virtual void myfunc() {}
    int int_a;
  };
} // namespace nsA

namespace nsB {
  class MyClass : public nsA::MyClass {
  public:
    virtual void myfunc() override {}
    std::vector<int> vec_b;
  };
} // namespace nsB

namespace nsC {
  class MyClass : public nsB::MyClass {
  public:
    virtual void myfunc() override {}
    int int_c;
  };
} // namespace nsC