QMenuBar: Mark items as dirty when switching away from native menu bar

QMenuBarPrivate::updateGeometries() returns early if the native menu
bar is in use, skipping the call to calcActionRects, so the action
rects are not in sync with the actions in this mode.

When switching to non-native menu bars, we would then crash in
QMenuBar::minimumSizeHint() because we're iterating the action
rects assuming the match the actions.

To fix this we need to ensure the action rects are computed by our
call to updateGeometries() in setNativeMenuBar(), which we can do
by explicitly marking the items as dirty.

Note that it's currently not possible to switch back to the native
menu bar, as the native menu bar is populated in QMenuBar::actionEvent
via QEvent::ActionAdded, and we're not doing anything to re-add
these actions once we've recreated the native menu bar.

Fixes: QTBUG-102107
Pick-to: 6.5 6.4 6.2
Change-Id: I7cf2b25539da633727693f5894ea22ea0d0d9aa5
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@qt.io>

src/widgets/widgets/qmenubar.cpp

@@ -1772,6 +1772,7 @@ void QMenuBar::setNativeMenuBar(bool nativeMenuBar)
         if (!nativeMenuBar) {
             delete d->platformMenuBar;
             d->platformMenuBar = nullptr;
+            d->itemsDirty = true;
         } else {
             if (!d->platformMenuBar)
                 d->platformMenuBar = QGuiApplicationPrivate::platformTheme()->createPlatformMenuBar();