Make rt.util.utf publicly available

[bauss]

On Monday, 3 December 2018 at 10:40:03 UTC, Eduard Staniloiu 
wrote:
> Hello, everyone.
>
> I've been looking over Phobos' `std.utf` and druntime's 
> `rt.util.utf` as there is some code duplication and I would 
> like to start removing that.
>
> I want to be able to import some of the existing druntime 
> functionality in Phobos, so we can remove the duplication: ex. 
> isValidDchar, toUTF*, etc.
>
> I'm not able to do so, since, as far as I can tell, the `rt` is 
> private: it's not part of the `druntime/import/` folder.
>
> Could you please tell me what's the reasoning behind this 
> decision and what would be the course of action going forward?
>
> Thank you,
> Edi

I think the reason behind the duplications is that the runtime 
shouldn't be dependent on Phobos and Phobos shouldn't be 
dependent on the runtime.

At least if I remember correctly about other duplications 
existing.