[Issue 21783] Add `if` as an operator

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=21783

--- Comment #1 from Bolpat <qs.il.paperinik at gmail.com> ---
It should have read:

> The best I could come up with is
> 
>     rhs ? lhs : true
> 
> which [...]

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