PR feedback: use descriptor property to avoid #ifs

Assets/Scripts/EyePoseVisualizer.cs

     {
         var faceManager = FindObjectOfType<ARFaceManager>();
         if (faceManager != null && faceManager.subsystem != null &&
-#if UNITY_2020_2_OR_NEWER
-            faceManager.subsystem.subsystemDescriptor.supportsEyeTracking)
-#else
-            faceManager.subsystem.SubsystemDescriptor.supportsEyeTracking)
-#endif
+            faceManager.descriptor.supportsEyeTracking)
         {
             m_FaceSubsystem = (XRFaceSubsystem)faceManager.subsystem;
             SetVisible((m_Face.trackingState == TrackingState.Tracking) && (ARSession.state > ARSessionState.Ready));

Assets/Scripts/EyeTrackingUI.cs

             m_Manager = FindObjectOfType<ARFaceManager>();
         }
         if (m_Manager != null && m_Manager.subsystem != null &&
-#if UNITY_2020_2_OR_NEWER
-            m_Manager.subsystem.subsystemDescriptor.supportsEyeTracking)
-#else
-            m_Manager.subsystem.SubsystemDescriptor.supportsEyeTracking)
-#endif
+            m_Manager.descriptor.supportsEyeTracking)
         {
             var infoGO = GetComponent<Text>();
             infoGO.text = "This device supports eye tracking.";

Assets/Scripts/FixationPoint2DVisualizer.cs

     {
         var faceManager = FindObjectOfType<ARFaceManager>();
         if (faceManager != null && faceManager.subsystem != null &&
-#if UNITY_2020_2_OR_NEWER
-            faceManager.subsystem.subsystemDescriptor.supportsEyeTracking)
-#else
-            faceManager.subsystem.SubsystemDescriptor.supportsEyeTracking)
-#endif
+            faceManager.descriptor.supportsEyeTracking)
         {
             m_FaceSubsystem = (XRFaceSubsystem)faceManager.subsystem;
             SetVisible((m_Face.trackingState == TrackingState.Tracking) && (ARSession.state > ARSessionState.Ready));