QSplashScreen: draw pixmap with SmoothTransfrom

Use high-quality scaling to improve rendering in cases
where the pixmap has to be scaled down, such as when
drawing a @2x pixmap at 150%.

Change-Id: I216b03b61dfa2cc2cc8c573e24a576424f6f5d17
Fixes: QTBUG-88982
Pick-to: 6.0 5.15
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>

src/widgets/widgets/qsplashscreen.cpp

@@ -353,6 +353,7 @@ bool QSplashScreen::event(QEvent *e)
     if (e->type() == QEvent::Paint) {
         Q_D(QSplashScreen);
         QPainter painter(this);
+        painter.setRenderHints(QPainter::SmoothPixmapTransform);
         painter.setLayoutDirection(layoutDirection());
         if (!d->pixmap.isNull())
             painter.drawPixmap(QPoint(), d->pixmap);