Guard the new articulated hand updates behind the UWP APIs being present

The new HandPose APIs will only work on V8 and beyond of the Windows SDK. We shouldn't try to invoke APIs/functionality unless the underlying platform actually supports that functionality.

Author: wiwei

Assets/MixedRealityToolkit.Providers/WindowsMixedReality/WindowsMixedRealityArticulatedHand.cs

@@ -15,6 +15,7 @@
 using Windows.Perception;
 using Windows.Perception.People;
 using Windows.UI.Input.Spatial;
+using Microsoft.MixedReality.Toolkit.Windows.Utilities;
 #endif
 
 namespace Microsoft.MixedReality.Toolkit.WindowsMixedReality.Input
@@ -220,6 +221,14 @@ protected override void UpdateControllerData(InteractionSourceState interactionS
             base.UpdateControllerData(interactionSourceState);
 
 #if WINDOWS_UWP
+            // The articulated hand support is only present in the 18361 version and beyond Windows
+            // SDK (which contains the V8 drop of the Universal API Contract). In particular,
+            // the HandPose related APIs are only present on this version and above.
+            if (!WindowsApiChecker.UniversalApiContractV8_IsAvailable)
+            {
+                return;
+            }
+
             PerceptionTimestamp perceptionTimestamp = PerceptionTimestampHelper.FromHistoricalTargetTime(DateTimeOffset.Now);
             IReadOnlyList<SpatialInteractionSourceState> sources = spatialInteractionManager?.GetDetectedSourcesAtTimestamp(perceptionTimestamp);
             foreach (SpatialInteractionSourceState sourceState in sources)