stubtest should warn about missing __del__

[JelleZijlstra]

Having __del__ present in stubs is useful for a few reasons:

• A subclass that calls super().__del__() would see a false positive if __del__ is present in the base class at runtime but not in the stub
• The documentation explicitly states that subclasses should call super().__del__() if they override a __del__ method. A type checker that wants to enforce this rule would need to know whether __del__ exists in the base class.

See discussion in python/typeshed#10984.

[hauntsaninja]

Who indeed cares ;-) https://github.com/python/mypy/pull/12203/files#diff-55639a1f38efeacbb10988649399037c13ad11e9c82890b453d98ea2bed9caf8R285

[AlexWaygood]

Who indeed cares ;-) https://github.com/python/mypy/pull/12203/files#diff-55639a1f38efeacbb10988649399037c13ad11e9c82890b453d98ea2bed9caf8R285

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