[UI] Add simple support for controller usage in UI

- Disabled unnecessary hotkeys thread when it is not used
- Removed problematic xam_exports static initialization
- Moved xam_dialogs_shown_ and xam_nui_dialogs_shown_ to XamState

src/xenia/kernel/xam/xam_ui.h

@@ -25,10 +25,9 @@ class XamDialog : public xe::ui::ImGuiDialog {
   }
 
  protected:
-  XamDialog(xe::ui::ImGuiDrawer* imgui_drawer)
-      : xe::ui::ImGuiDialog(imgui_drawer) {}
+  XamDialog(xe::ui::ImGuiDrawer* imgui_drawer);
 
-  virtual ~XamDialog() {}
+  ~XamDialog();
   void OnClose() override {
     if (close_callback_) {
       close_callback_();