New array Extension plus tests (#461)

* * Added new "InitialiseArray" array extension to set all values of an array to a new value, including Tests
* Added null check on Array AddItem
Fixed license in Core test 2

* Update XRTK-Core/Packages/com.xrtk.core/Extensions/ArrayExtensions.cs

Co-Authored-By: Stephen Hodgson <StephenHodgson@users.noreply.github.com>

* Applied review patches

Co-authored-by: Stephen Hodgson <StephenHodgson@users.noreply.github.com>

Extensions/ArrayExtensions.cs

@@ -37,12 +37,43 @@ public static bool IsValidArray(this Array array)
         /// <param name="array">The array to extend</param>
         /// <param name="newItem">The item to add to the array</param>
         /// <returns></returns>
-        public static T[] AddItem<T>(this T[] array, T newItem, int insertAtIndex = 0)
+        public static T[] AddItem<T>(this T[] array, T newItem)
         {
+            // Initialise the array if it is null
+            if (array == null)
+            {
+                return new[] { newItem };
+            }
+
+            //Extend the array, copy the items and add the new one
             var newArray = new T[array.Length + 1];
-            array.CopyTo(newArray, insertAtIndex);
+            array.CopyTo(newArray, 0);
             newArray[array.Length] = newItem;
             return newArray;
         }
+
+        /// <summary>
+        /// Initialises an array with a default item
+        /// </summary>
+        /// <typeparam name="T"></typeparam>
+        /// <param name="array">The array to initialise</param>
+        /// <param name="newItem">The default item to set all the array items to</param>
+        /// <returns></returns>
+        public static T[] InitialiseArray<T>(this T[] array, T newItem)
+        {
+            // Initialise the array if it is null
+            if (array == null)
+            {
+                return new[] { newItem };
+            }
+
+            //Set all the items to the provided value
+            for (int i = 0; i < array.Length; i++)
+            {
+                array[i] = newItem;
+            }
+
+            return array;
+        }
     }
-}
+}