Actually reuse these structs via ref

Author: keveleigh

org.mixedrealitytoolkit.input/Subsystems/HandsAggregator/MRTKHandsAggregatorSubsystem.cs

@@ -259,7 +259,7 @@ public override bool TryGetPinchingPoint(XRNode handNode, out HandJointPose join
                 gotData &= TryGetJoint(TrackedHandJoint.IndexTip, handNode, out HandJointPose indexPose);
                 gotData &= TryGetJoint(TrackedHandJoint.Palm, handNode, out HandJointPose palmPose);
 
-                HandJointPose pinchPointPose = handNode == XRNode.LeftHand ? leftPinchPose : rightPinchPose;
+                ref HandJointPose pinchPointPose = ref (handNode == XRNode.LeftHand ? ref leftPinchPose : ref rightPinchPose);
 
                 // Stabilize the pinch pose by a weighted average between the thumb and index.
                 // A true average (50% thumb, 50% index) is too unstable for precise manipulation.