Added a visible state to QWindow

(cherry picked from commit 6cd96d1921af9740bf92405ae3adf466140f8923)

src/gui/kernel/qwindow_qpa.cpp

@@ -60,6 +60,7 @@ public:
         , windowFlags(Qt::Window)
         , surfaceType(QWindow::RasterSurface)
         , platformWindow(0)
+        , visible(false)
         , glContext(0)
         , widget(0)
     {
@@ -75,6 +76,7 @@ public:
     QWindow::SurfaceType surfaceType;
 
     QPlatformWindow *platformWindow;
+    bool visible;
     QWindowFormat requestedFormat;
     QString windowTitle;
     QRect geometry;
@@ -116,6 +118,13 @@ void QWindow::setVisible(bool visible)
     d->platformWindow->setVisible(visible);
 }
 
+bool QWindow::visible() const
+{
+    Q_D(const QWindow);
+
+    return d->visible;
+}
+
 void QWindow::create()
 {
     Q_D(QWindow);

src/gui/kernel/qwindow_qpa.h

@@ -89,6 +89,8 @@ public:
     void setWidget(QWidget *widget);
 
     void setVisible(bool visible);
+    bool visible() const;
+
     void create();
 
     WId winId() const;