Indicates whether the user is present and interacting with the device.
Many XR devices such as HMDs can detect whether the user is currently wearing and/or interacting with the device. This property can be used to test the state of this user interaction. The exact behavior of this property will vary with each type of device -- some devices will have a sensor specifically to detect user proximity, and users will rely on movement, but applications can reasonably infer that a user is present with the device when the property is UserPresenceState.Present.