[Issue 20310] std.json to(Pretty)String not pure

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=20310

--- Comment #1 from Robert Schadek <rschadek at symmetryinvestments.com> ---
depends on https://issues.dlang.org/show_bug.cgi?id=15321

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