View::closeWindow() is no longer virtual.

Implementation is common to all frontends.
Renamed it to closeRootView() to be consistent.

src/qtwidgets/views/ViewWrapper_qtwidgets.h

@@ -46,7 +46,7 @@ public:
     std::shared_ptr<ViewWrapper> rootView() const override;
     std::shared_ptr<ViewWrapper> parentView() const override;
     void setParent(View *) override;
-
+    bool close() override;
     std::shared_ptr<ViewWrapper> childViewAt(QPoint localPos) const override;
     QVector<std::shared_ptr<View>> childViews() const override;
     HANDLE handle() const override;