Follow up on PR 1200 which introduced this sniff.

> This sniff will throw an error, even when there is no destructor as a destructor may be declared in a parent class.
> 👉 We could reduce the potential noise from this sniff a little further by only throwing the error when the class either contains a __destruct() method or extends a parent class. Should we ?

This PR implements the above by:
* Checking for a `__destruct()` method. If one is found, an error will be thrown.
* If no `__destruct()` method was found, but the class either extends another class or `use`s a trait, it will throw a _warning_ instead as a `__destruct()` method may still be declared in the parent class or the trait.
* If no `__destruct()` method is found and the class does not extend another, nor use `trait`s, the sniff will stay silent.

Includes implementing protection against false positives for calls to `exit()` found in nested closed constructs within a `__construct()` method.
Includes efficiency tweaks to in case of large `__construct()` methods with high code complexity.