可用于确定 XR 设备是否处于活动状态的只读值。
When true, Unity accepts input from the device and attempts to render to the device's display(s). Note that this returns true even if the device is not currently rendering due to lack of user presence (see XRDevice.userPresence). This can become false if a device is disconnected, could not be initialized (see XRSettings.LoadDeviceByName), or XRSettings.enabled is set to false.
XR 输出将自动镜像到主显示器（如果适用）。这可以通过 XRSettings.showDeviceView 进行控制。
主窗口仍然由 Screen 和相关 API 控制。