[Development] Updated high-DPI support for Qt 5.14

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> On 16 Sep 2019, at 15:21, Florian Bruhin <me at the-compiler.org> wrote:
> 
> Looks like that change didn't add a changelog entry and didn't bother to update
> the documentation at all…

I’ve updated https://wiki.qt.io/New_Features_in_Qt_5.14 . We’ll add similar content to the change log once it gets posted.

The documentation (https://doc.qt.io/qt-5/highdpi.html) is in practice append-only at this point and needs a ground-up rewrite. I’ve pushed a minimal update with the new options here: https://codereview.qt-project.org/c/qt/qtdoc/+/275028


(Does anyone want to help updating the high-dpi docs? Let me know.)

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