plugins/qpa: Suppress warnings about raise()/lower() not being implemented

We write window code with an assumption that the compositor will do the
right thing when a window is shown or hidden or activated, so our qpa can
leave stub implementations for raise() and lower() to suppress the
warnings produced by the stack manipulation functions in Qt.

src/plugins/qpa/window.cpp

@@ -111,6 +111,16 @@ void Window::requestActivateWindow()
 #endif
 }
 
+void Window::raise()
+{
+    // Left blank intentionally to suppress warnings in QPlatformWindow::raise().
+}
+
+void Window::lower()
+{
+    // Left blank intentionally to suppress warnings in QPlatformWindow::lower().
+}
+
 void Window::setGeometry(const QRect &rect)
 {
     const QRect oldGeometry = geometry();

src/plugins/qpa/window.h

@@ -36,6 +36,8 @@ public:
     WId winId() const override;
     qreal devicePixelRatio() const override;
     void requestActivateWindow() override;
+    void raise() override;
+    void lower() override;
 
     InternalWindow *internalWindow() const;
     Swapchain *swapchain(const std::shared_ptr<EglContext> &context, const QHash<uint32_t, QList<uint64_t>> &formats);