[UI] Fixed issues with ImGui on Vulkan and few ASAN issues related to ImGui

- Simplified handling of notifications to faster version with ranges
- Removed usage of STB sprintf on checked due to ASAN violation
- Draw ImGui windows only when they're not in close_pending state

src/xenia/ui/imgui_dialog.h

@@ -34,6 +34,8 @@ class ImGuiDialog {
 
   void Draw();
 
+  bool IsClosing() const { return has_close_pending_; }
+
  protected:
   ImGuiDialog(ImGuiDrawer* imgui_drawer);