[Issue 18187] std.uni.Grapheme should be usable in @safe

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=18187

--- Comment #3 from John Colvin <john.loughran.colvin at gmail.com> ---
https://github.com/dlang/phobos/pull/6330

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