Qt: Replace QWindow for display with QWidget base

Not as elegant, but it solves the input focus issue.

src/duckstation-qt/qtdisplaywidget.h

@@ -0,0 +1,50 @@
+#pragma once
+#include "common/types.h"
+#include <QtWidgets/QWidget>
+
+class QKeyEvent;
+class QResizeEvent;
+
+class HostDisplay;
+
+class QtHostInterface;
+
+class QtDisplayWidget : public QWidget
+{
+  Q_OBJECT
+
+public:
+  QtDisplayWidget(QtHostInterface* host_interface, QWidget* parent);
+  virtual ~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();
+
+  virtual void Render() = 0;
+
+  // this comes back on the emu thread
+  virtual void windowResized(s32 new_window_width, s32 new_window_height);
+
+  virtual QPaintEngine* paintEngine() const override;
+
+Q_SIGNALS:
+  void windowResizedEvent(int width, int height);
+
+protected:
+  qreal getDevicePixelRatioFromScreen() const;
+  int getScaledWindowWidth() const;
+  int getScaledWindowHeight() const;
+
+  virtual bool createImGuiContext();
+  virtual void destroyImGuiContext();
+  virtual bool createDeviceResources();
+  virtual void destroyDeviceResources();
+
+  virtual bool event(QEvent* event) override;
+
+  QtHostInterface* m_host_interface;
+};