Fix not working popup with qquick on eglfs

After refactoring in 5d1ef38 we lost popups with qquick.
Unfortunately we do not have tests for it as we do
not run eglfs on ci.

Pick-to: 6.8 6.7
Fixes: QTBUG-119908
Change-Id: Iea6cadf96dcac488898bb31132938fe8020d4d79
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@qt.io>

src/webenginequick/api/qquickwebengineview.cpp

@@ -261,8 +261,9 @@ class WebEngineQuickWidgetDelegate : public QtWebEngineCore::WidgetDelegate
 
     void InitAsPopup(const QRect &screenRect) override
     {
-        Q_UNUSED(screenRect);
-        Q_UNREACHABLE();
+        // note this is called when there is no windowing system
+        // otherwsie see RenderWidgetHostViewQtDelegateQuickWindow
+        m_contentItem->setPosition(screenRect.topLeft());
     }
 
     void Bind(WebContentsAdapterClient *client) override