DYN-6440 Custom Selection node overlapping Code Review

Added more comments for clarifying the use of the IsVisibleDropDownTextBlock  property.
Also I've added the Dispose() method for unsubscribing event handlers (although I'm not so sure if we are disposing this class correctly).

src/Libraries/CoreNodeModelsWpf/NodeViewCustomizations/CustomSelection.cs

@@ -6,6 +6,8 @@
 using Dynamo.Wpf;
 using CoreNodeModels;
 using System.Windows.Data;
+using System.Data.Common;
+using System;
 
 namespace CoreNodeModelsWpf.Nodes
 {
@@ -14,6 +16,7 @@ namespace CoreNodeModelsWpf.Nodes
     /// </summary>
     public class CustomSelectionNodeViewCustomization : DropDownNodeViewCustomization, INodeViewCustomization<CustomSelection>
     {
+        private CustomSelectionControl formControl;
         /// <summary>
         /// Customize the visual appearance of the custom dropdown node.
         /// </summary>
@@ -22,7 +25,7 @@ public class CustomSelectionNodeViewCustomization : DropDownNodeViewCustomizatio
         public void CustomizeView(CustomSelection model, NodeView nodeView)
         {
             const double leftMargin = 40;
-            var formControl = new CustomSelectionControl(new CustomSelectionViewModel(model));
+            formControl = new CustomSelectionControl(new CustomSelectionViewModel(model));
 
             nodeView.inputGrid.Children.Add(formControl);
 
@@ -43,6 +46,8 @@ public void CustomizeView(CustomSelection model, NodeView nodeView)
             var dropDownTextBlock = dropdown.Template.FindName("PART_ReadOnlyTextBlock", dropdown) as TextBlock;
             if (dropDownTextBlock != null)
             {
+                //IsVisibleDropDownTextBlock will be false by default so the TextBlock (located in the ComboBox template) will be Collapsed then just when is a Custom Selection node we set the value to true and the TextBlock will be visible
+                //We used a TextBlock because the normal TextBox doesn't have the TextTrimming property and the requirement was asking for setting TextTrimming="CharacterEllipsis"
                 model.IsVisibleDropDownTextBlock = true;
             }
 
@@ -69,5 +74,19 @@ private void BaseComboBox_SelectionChanged(object sender, SelectionChangedEventA
                 comboSender.ToolTip = comboSender.SelectedItem?.ToString();
             }           
         }
+
+        public void Dispose()
+        {
+            Dispose(true);
+            GC.SuppressFinalize(this);
+        }
+
+        protected void Dispose(bool disposing)
+        {
+            if (disposing)
+            {
+                formControl.BaseComboBox.SelectionChanged -= BaseComboBox_SelectionChanged;
+            }
+        }
     }
 }