`A2-7-3`: Friend functions in template classes do not recognise documentation

### Affected rules
 - `A2-7-3`

### Description

Friend functions in template classes do not detect documentation.

### Example

```cpp
template <typename T> class ClassG {
  private:
    int x;
  public:
  // Documentation
  friend int foo(ClassG<T> g) {
    return g.x;
  }
};

void test() {
  ClassG<int> g;
  foo(g);
}
```
