[Issue 13155] Disallow final abstract classes

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=13155

--- Comment #1 from Sobirari Muhomori <dfj1esp02 at sneakemail.com> ---
In C# it's not an error, but a normal idiom when a class should not be
inherited and instances should not be created.

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