[clang-format] [PR34574] Handle [[nodiscard]] attribute in class declaration

Summary:
https://bugs.llvm.org/show_bug.cgi?id=34574
https://bugs.llvm.org/show_bug.cgi?id=38401

```
template <typename T>
class [[nodiscard]] result
{
  public:
    result(T&&)
    {
    }
};
```

formats incorrectly to

```
template <typename T>
class [[nodiscard]] result{public : result(T &&){}};
```

Reviewed By: krasimir

Subscribers: cfe-commits

Tags: #clang, #clang-format

Differential Revision: https://reviews.llvm.org/D79354