[cxx-interop][regression] methods returning vector are unsafe unless vector instantiated prior in a type alias.

[hyp]

After #64897 our safe/unsafe method detection logic has regressed .

For example, let's say we're returning a vector:

class SimplePOD {
public:
    int x;
};

class VecOwner {
public:
    std::vector<SimplePOD> getPODItems() const;
};

The module interface will mark the method as unsafe:

struct VecOwner {
  init()
  func __getPODItemsUnsafe() -> std.__1.vector<SimplePOD, allocator<SimplePOD>>
  @available(swift, obsoleted: 5, renamed: "__getPODItemsUnsafe()")
  func getPODItems() -> std.__1.vector<SimplePOD, allocator<SimplePOD>>
}

[hyp]

workaround, instantiate the vector template in a type alias.

[hyp]

we should revert #64897 for now.