For GDI, there doesn't seem to be any way to do this, so it depends
on selecting the DirectWrite font database explicitly.
This moves the supportsVariableApplicationFonts() check into the
QPlatformFontDatabase instead of the font engine, since that's
where it belongs.
[ChangeLog][Fonts] Added support for selecting named instances in
variable application fonts when using the DirectWrite backend.
Task-number: QTBUG-108624
Change-Id: I51e0fedd7a9616088a06453a1d17f48bd18fa5a7
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@qt.io>
500be123f4