COMPMID-2076: Add StackLayer to the graph API

Change-Id: Ifae23659c2471d9c052bc8adf066c5228d6e8b23
Signed-off-by: Michele Di Giorgio <michele.digiorgio@arm.com>
Reviewed-on: https://review.mlplatform.org/c/893
Tested-by: Arm Jenkins <bsgcomp@arm.com>
Reviewed-by: Georgios Pinitas <georgios.pinitas@arm.com>
Comments-Addressed: Arm Jenkins <bsgcomp@arm.com>
diff --git a/arm_compute/graph/INodeVisitor.h b/arm_compute/graph/INodeVisitor.h
index 842ca4b..291fe7c 100644
--- a/arm_compute/graph/INodeVisitor.h
+++ b/arm_compute/graph/INodeVisitor.h
@@ -141,6 +141,11 @@
      * @param[in] n Node to visit.
      */
     virtual void visit(SplitLayerNode &n) = 0;
+    /** Visit StackLayerNode.
+     *
+     * @param[in] n Node to visit.
+     */
+    virtual void visit(StackLayerNode &n) = 0;
 };
 
 /** Default visitor implementation
@@ -240,6 +245,10 @@
     {
         default_visit();
     }
+    virtual void visit(StackLayerNode &n) override
+    {
+        default_visit();
+    }
 #endif /* DOXYGEN_SKIP_THIS */
 
     /** Function to be overloaded by the client and implement default behavior for the