Fix S1128 FN: unused using alias directives

[cristian-ambrosini-sonarsource]

The rule does not take into account for unnecessary using alias directives to alias tuple types, array types, pointer types, or other unsafe types.

using Person = (string name, string surname); // FN
using unsafe IntPointerExt = int*; // FN
using IntArray = int[]; // FN

namespace ANamespace
{
    using Point2D = (int, int); // FN
    using unsafe IntPointer = int*; // FN: unused
}

[cristian-ambrosini-sonarsource]

I'm moving back this task to 'ToDo' as we propose to align the rule with Roslyn's CS8019 interception. For more details, please refer to this Scanner issue. This proposed solution would address this issue, along with all other open issues associated with this rule.