Fix #11167 FP virtual call in destructor even though class is final / Delete 'final' from specializations

[chrchr-github]

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[firewave]

Actually this is not a "keyword" per spec but an "identifier with special meaning" - see https://en.cppreference.com/w/cpp/keyword.

There's others which also need to be handled. And I wonder if this also needs to be done in other places. Or if those need special handling.

Will also incorporate this into #3774 when the handling is clear.

[chrchr-github]

Good catch. It seems that we normally remove final, e.g. in struct S final {};. So the TemplateSimplifier needs to also remove final in instantiations.