Translate _d_delstruct to template

[teodutu]

This implements a template version of _d_delstruct to replace the homonymous function from rt.lifetime.d.

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[PetarKirov]

Can you refactor the original (non-template) version of the hook to call the new (template) one?

That way, the change would be easier to review, since the net result would be that most of the code would be moved to a new function and all of the existing tests would still exercise the code paths.

[teodutu]

Can you refactor the original (non-template) version of the hook to call the new (template) one?

The signature of the old hook is this:

extern (C) void _d_delstruct(void** p, TypeInfo_Struct inf) @weak

In order to call the new hook from it, I would need to cast *p to the correct type, which I cannot do. So I don't think I can make this change.

[PetarKirov]

You're right. For some reason I didn't check carefully the new implementation, but instead I assumed that it would use the same typeinfo-based logic that this would later be changed to template-driven, which I see you have already done.