fix(Interaction): ensure trigger collision check is done every frame

Previously, the `triggerIsColliding` bool was only set if an object
wasn't being touched which would cause the `StopTouching` method to
execute which caused problems with using objects.

This has now been fixed so the bool is set every `OnTriggerStay`
if no object is being touched or if the object being touched is the
same as the current touched object.

Assets/VRTK/Scripts/Interactions/VRTK_InteractTouch.cs

@@ -295,9 +295,14 @@ private void OnTriggerExit(Collider collider)
         private void OnTriggerStay(Collider collider)
         {
             var colliderInteractableObject = TriggerStart(collider);
-            if (touchedObject == null && colliderInteractableObject && IsObjectInteractable(collider.gameObject))
+
+            if (touchedObject == null || touchedObject == collider.gameObject)
             {
                 triggerIsColliding = true;
+            }
+
+            if (touchedObject == null && colliderInteractableObject && IsObjectInteractable(collider.gameObject))
+            {
                 touchedObject = colliderInteractableObject;
                 var touchedObjectScript = touchedObject.GetComponent<VRTK_InteractableObject>();
                 var touchingObject = gameObject;