[util] Add moving append() call to vector

Add a version of `append()` that takes an rvalue reference.

src/libraries/util/util/vector.h

@@ -117,6 +117,16 @@ public:
         return m_elements[m_size++];
     }
 
+    /// Add an item onto the array by copying it.
+    /// \arg item  The item to add
+    /// \returns   A reference to the added item
+    T & append(T &&item)
+    {
+        ensure_capacity(m_size + 1);
+        m_elements[m_size] = std::move(item);
+        return m_elements[m_size++];
+    }
+
     /// Construct an item in place onto the end of the array.
     /// \returns   A reference to the added item
     template <typename... Args>