qtquick: Fix showing qtquick window not setting the root item visible

src/qtquick/Window_qtquick.cpp

@@ -69,3 +69,10 @@ Window::Ptr Window_qtquick::transientParent() const
 
     return nullptr;
 }
+
+void Window_qtquick::setVisible(bool is)
+{
+    Window_qt::setVisible(is);
+    if (auto root = rootView())
+        root->setVisible(is);
+}

src/qtquick/Window_qtquick.h

@@ -21,6 +21,7 @@ public:
     ~Window_qtquick();
     std::shared_ptr<ViewWrapper> rootView() const override;
     Window::Ptr transientParent() const override;
+    void setVisible(bool) override;
 };
 
 }

tests/tst_docks.cpp

@@ -4321,6 +4321,8 @@ void TestDocks::tst_moreTitleBarCornerCases()
         delete fw1; // the old window
 
         fw1 = dock1->floatingWindow();
+        QVERIFY(fw1);
+        QVERIFY(fw1->isVisible());
         QVERIFY(dock1->isVisible());
         QVERIFY(!dock1->dptr()->frame()->titleBar()->isVisible());
         QVERIFY(fw1->titleBar()->isVisible());