```
Enables high-DPI scaling in Qt on supported platforms (see also High DPI
Displays). Supported platforms are X11, Windows and Android. Enabling
makes Qt scale the main (device independent) coordinate system according
to display scale factors provided by the operating system. This
corresponds to setting the QT_AUTO_SCREEN_SCALE_FACTOR environment
variable to 1. This attribute must be set before QGuiApplication is
constructed. This value was added in Qt 5.6.
```
Backport of core PR16254.
Fixes https://github.com/Bitcoin-ABC/bitcoin-abc/issues/378