Rather than have a fontChanged() signal which can be connected to for
tracking when the application font has changed, then it is better to
use the event that is sent to all windows and the application itself.
That way it is easy for a window/widget or item that cares about the
change to the application font to catch it in the event() function.
[ChangeLog][QtGui][QGuiApplication] Deprecated fontChanged() signal in
favor of QEvent::ApplicationFontChanged.
Change-Id: Iae8e832238fc85e385a52305bc04f16e597454b0
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>
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