UltimateXR Demo For Pico

It's a basic attempt to apply Ultimate XR framwork on Pico.
Known issues:
- Unsatisfying lighting quality because of the heaviness of the demo scene.
- Bugs with controller buttons after a pause, like pressing home button and resume the app.
More about Ultimate XR: https://www.ultimatexr.io/

这是Ultimate XR在Pico上的尝试应用
已知问题：
- 因为场景过大引起的光照效果不佳；
- 应用暂停后引起的控制器按钮Bug, 比如按下Home键暂停然后继续应用后；
了解更多关于 Ultimate XR:https://www.ultimatexr.io/