[Issue 13972] Make scoped, Unique, and RefCounted @nogc

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=13972

--- Comment #6 from weaselcat <r9shackleford at gmail.com> ---
RefCounted almost done.
https://github.com/D-Programming-Language/phobos/pull/3171 made it possible to
make @nogc refcounted types, but destroy still doesn't infer attributes as per
https://github.com/D-Programming-Language/druntime/pull/1181

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