[Issue 15888] std.format should not produce deprecated hexstrings

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=15888

Berni44 <bugzilla at bernis-buecher.de> changed:

           What    |Removed                     |Added
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            Summary|std.format generates broken |std.format should not
                   |hex strings for wchar[] and |produce deprecated
                   |dchar[] with invalid values |hexstrings

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