[clang-tidy] report redundant `class`/`struct`/`union`/`enum` tag in declarations with C++

```cpp
struct Struct {};
class Class {};
union Union {};
enum Enum{};

void f()
{
struct Struct S;
class Class C;
union Union U;
enum Enum E;
}
```

https://godbolt.org/z/hPGn1ePfx

In C++ it is unnecessary to specify the `class`/`struct`/`union`/`enum` tag.