Fix S3897: Correctly recognize IEquatable<T> implementations from base classes

[valhristov]

Investigate why the following code is not compliant and provide a fix:

class MyClass : IEquatable<MyClass> // Compliant
{
    public override bool Equals(object obj)
    {
        return Equals(obj as MyClass);
    }
    public bool Equals(MyClass other)
    {
        return true;
    }
}

class SubClass : MyClass, IEquatable<SubClass> // Compliant?
{
    public override bool Equals(object obj)
    {
        return Equals(obj as SubClass);
    }
    public bool Equals(SubClass other)
    {
        return true;
    }
}

Source

[overeemm]

I've attempted to fix this, but it isn't complete yet. #429

[Evangelink]

This is fixed by #464