[clang-tidy] detect `const`-qualified member functions which are not physically const

```cpp
struct SS
{
void fn();
};

struct S
{
void fn() const
{
m_ss->fn(); // allowed but breaks constness
}
private:
SS* m_ss;
};
```

The code above is valid but the constness of the called function is misleading.

This could be mitigated using [std::experimental::propagate_const](https://en.cppreference.com/cpp/experimental/propagate_const) for `S::m_ss`.