Qt: Refactor render widget state transitions

Recreate widget each time. Fixes fullscreen mode switches on D3D11 and
hopefully Wayland.

src/duckstation-qt/qtdisplaywidget.h

@@ -2,49 +2,26 @@
 #include "common/types.h"
 #include <QtWidgets/QWidget>
 
-class QKeyEvent;
-class QResizeEvent;
-
-class HostDisplay;
-
-class QtHostInterface;
-
-class QtDisplayWidget : public QWidget
+class QtDisplayWidget final : public QWidget
 {
   Q_OBJECT
 
 public:
-  QtDisplayWidget(QtHostInterface* host_interface, QWidget* parent);
-  virtual ~QtDisplayWidget();
+  QtDisplayWidget(QWidget* parent);
+  ~QtDisplayWidget();
 
-  virtual HostDisplay* getHostDisplayInterface();
-
-  virtual bool hasDeviceContext() const;
-  virtual bool createDeviceContext(QThread* worker_thread, bool debug_device);
-  virtual bool initializeDeviceContext(bool debug_device);
-  virtual void destroyDeviceContext();
-
-  // this comes back on the emu thread
-  virtual void windowResized(s32 new_window_width, s32 new_window_height);
-
-  virtual QPaintEngine* paintEngine() const override;
+  QPaintEngine* paintEngine() const override;
 
   int scaledWindowWidth() const;
   int scaledWindowHeight() const;
+  qreal devicePixelRatioFromScreen() const;
 
 Q_SIGNALS:
   void windowResizedEvent(int width, int height);
   void windowRestoredEvent();
+  void windowClosedEvent();
+  void windowKeyEvent(int key_code, bool pressed);
 
 protected:
-  qreal devicePixelRatioFromScreen() const;
-
-  virtual bool createImGuiContext();
-  virtual void destroyImGuiContext();
-  virtual bool createDeviceResources();
-  virtual void destroyDeviceResources();
-
-  virtual bool event(QEvent* event) override;
-
-  QtHostInterface* m_host_interface;
+  bool event(QEvent* event) override;
 };