Should an unqualified interface member allow two dispatch paths?

For example:

```c++
struct Interface {
int foo();
};

struct A {
int foo() && { return 1; }
int foo() & { return 2; }
};

protocol p{A{}};
p.foo(); // 2.
std::move(p).foo(); // 1?
```

This would require us to generate two vtable entries for `int foo()`. Alternatively, we could say that `T` only conforms if it provides `int foo()` as one member function without overloading.

Start with the protocol example and trace how an unqualified Interface::foo is represented, how A's ref-qualified overloads are checked, and how dispatch is selected. Compare the two alternatives in the issue—two vtable entries or requiring one unoverloaded member—and document the chosen conformance and dispatch behavior for both calls.

Written by the indexing model from the issue text.