ui: Add menubar backend selection

Author: mborgerson

ui/xui/menubar.cc

@@ -168,6 +168,15 @@ void ShowMainMenu()
                     g_config.display.ui.scale = ui_scale_idx;
                 }
             }
+
+            ImGui::Combo("Backend", &g_config.display.renderer,
+                 "Null\0"
+                 "OpenGL\0"
+#ifdef CONFIG_VULKAN
+                 "Vulkan\0"
+#endif
+                );
+
             int rendering_scale = nv2a_get_surface_scale_factor() - 1;
             if (ImGui::Combo("Int. Resolution Scale", &rendering_scale,
                              "1x\0"