Add active loader checking for OpenXR

Author: keveleigh

Assets/MRTK/Providers/OpenXR/MRTK.OpenXR.asmdef

@@ -5,6 +5,7 @@
         "Microsoft.MixedReality.OpenXR",
         "Microsoft.MixedReality.Toolkit",
         "Microsoft.MixedReality.Toolkit.Providers.XRSDK",
+        "Unity.XR.Management",
         "Unity.XR.OpenXR"
     ],
     "includePlatforms": [

Assets/MRTK/Providers/OpenXR/Scripts/OpenXRDeviceManager.cs

@@ -8,6 +8,10 @@
 using Unity.Profiling;
 using UnityEngine.XR;
 
+#if UNITY_OPENXR
+using UnityEngine.XR.OpenXR;
+#endif // UNITY_OPENXR
+
 namespace Microsoft.MixedReality.Toolkit.XRSDK.OpenXR
 {
     [MixedRealityDataProvider(
@@ -29,6 +33,34 @@ public OpenXRDeviceManager(
             uint priority = DefaultPriority,
             BaseMixedRealityProfile profile = null) : base(inputSystem, name, priority, profile) { }
 
+        private bool? isActiveLoader = null;
+        private bool IsActiveLoader
+        {
+            get
+            {
+#if UNITY_OPENXR
+                if (!isActiveLoader.HasValue)
+                {
+                    isActiveLoader = IsLoaderActive<OpenXRLoader>();
+                }
+#endif // UNITY_OPENXR
+
+                return isActiveLoader ?? false;
+            }
+        }
+
+        /// <inheritdoc />
+        public override void Enable()
+        {
+            if (!IsActiveLoader)
+            {
+                IsEnabled = false;
+                return;
+            }
+
+            base.Enable();
+        }
+
         #region Controller Utilities
 
         private static readonly ProfilerMarker GetOrAddControllerPerfMarker = new ProfilerMarker("[MRTK] OpenXRDeviceManager.GetOrAddController");