MainWindow: shutdown different input interfaces

`MainWindow` initializes a number of input interfaces but never shuts
them down. This was causing a crash-after-exit on macOS where the
ControllerInterface backend stores a `std::thread` object in a static
variable and only stops it when ControllerInterface::Shutdown is called.

Source/Core/DolphinQt2/MainWindow.cpp

@@ -52,6 +52,7 @@ MainWindow::MainWindow() : QMainWindow(nullptr)
 MainWindow::~MainWindow()
 {
   m_render_widget->deleteLater();
+  ShutdownControllers();
 }
 
 void MainWindow::InitControllers()
@@ -66,6 +67,15 @@ void MainWindow::InitControllers()
   HotkeyManagerEmu::Initialize();
 }
 
+void MainWindow::ShutdownControllers()
+{
+  g_controller_interface.Shutdown();
+  Pad::Shutdown();
+  Keyboard::Shutdown();
+  Wiimote::Shutdown();
+  HotkeyManagerEmu::Shutdown();
+}
+
 void MainWindow::CreateComponents()
 {
   m_menu_bar = new MenuBar(this);

Source/Core/DolphinQt2/MainWindow.h

@@ -66,6 +66,7 @@ private:
   void ConnectPathsDialog();
 
   void InitControllers();
+  void ShutdownControllers();
 
   void StartGame(const QString& path);
   void ShowRenderWidget();