Client: Use a pixel font size for window decorations

The window title bar's height is given in device pixels, so the font
size should be as well.

Task-number: QTBUG-68834
Change-Id: I5a82deb39439088dd55152fb8bae5c2d19d8b33e
Reviewed-by: Paul Olav Tvete <paul.tvete@qt.io>
Reviewed-by: Pier Luigi Fiorini <pierluigi.fiorini@liri.io>

src/plugins/platforms/wayland/plugins/decorations/bradient/main.cpp

@@ -255,6 +255,7 @@ void QWaylandBradientDecoration::paint(QPaintDevice *device)
         int dy = (top.height()- size.height()) /2;
         QFont font = p.font();
         font.setBold(true);
+        font.setPixelSize(12);
         p.setFont(font);
         QPoint windowTitlePoint(top.topLeft().x() + dx,
                  top.topLeft().y() + dy);