Function onXRSessionStart

onXRSessionStart(fn: (evt: XRSessionEventArgs) => void): () => void
Add a listener for when an XR session starts This event is triggered when the XR session is started, either by the user or by the application before all other XR start events
Parameters
- fn: (evt: XRSessionEventArgs) => void
  The function to call when the XR session starts
Returns () => void
A function to remove the listener
Example
```
onXRSessionStart((evt) => {
  console.log("XR session started", evt);
});
```