[clang] [Clang][Sema] Fix crash when using name of UnresolvedUsingValueDecl with template arguments (PR #83842)

[Krystian Stasiowski via cfe-commits]

sdkrystian wrote:

@wlei-llvm Thank you! I've reduced the repro to this:
```cpp
struct A { };

template<typename T>
void f(A);

struct B {
  void f();

  void g() {
    f<int>(A());
  }
};
```

https://github.com/llvm/llvm-project/pull/83842