Added KeyUp event in TextBoxBase

Source/Engine/UI/GUI/Common/TextBoxBase.cs

@@ -134,6 +134,11 @@ namespace FlaxEngine.GUI
         /// </summary>
         public event Action<KeyboardKeys> KeyDown;
 
+        /// <summary>
+        /// Event fired when a key is up.
+        /// </summary>
+        public event Action<KeyboardKeys> KeyUp; 
+
         /// <summary>
         /// Gets or sets a value indicating whether this is a multiline text box control.
         /// </summary>
@@ -1173,6 +1178,13 @@ namespace FlaxEngine.GUI
             return true;
         }
 
+        /// <inheritdoc />
+        public override void OnKeyUp(KeyboardKeys key)
+        {
+            base.OnKeyUp(key);
+            KeyUp?.Invoke(key);
+        }
+
         /// <inheritdoc />
         public override bool OnKeyDown(KeyboardKeys key)
         {