Fix regression that caused us to not update hte builder text as the user typed.

src/EditorFeatures/Core/Implementation/IntelliSense/Completion/Presentation/CustomCommitCompletion.cs

@@ -19,12 +19,10 @@ internal sealed class CustomCommitCompletion : Completion3, ICustomCommit
         private readonly CompletionPresenterSession _completionPresenterSession;
         internal readonly CompletionItem CompletionItem;
         private readonly ImageMoniker _imageMoniker;
-        private readonly string _displayText;
 
         public CustomCommitCompletion(
             CompletionPresenterSession completionPresenterSession,
-            CompletionItem completionItem,
-            string displayText)
+            CompletionItem completionItem)
         {
             // PERF: Note that the base class contains a constructor taking the displayText string
             // but we're intentionally NOT using that here because it allocates a private CompletionState
@@ -32,7 +30,6 @@ internal sealed class CustomCommitCompletion : Completion3, ICustomCommit
             // extra allocation is avoided.
             _completionPresenterSession = completionPresenterSession;
             this.CompletionItem = completionItem;
-            _displayText = displayText ?? completionItem.DisplayText;
             _imageMoniker = ImageMonikers.GetImageMoniker(CompletionItem.Tags);
         }
 
@@ -44,7 +41,7 @@ public void Commit()
             _completionPresenterSession.OnCompletionItemCommitted(CompletionItem);
         }
 
-        public override string DisplayText => _displayText;
+        public override string DisplayText { get; set; }
 
         public override string InsertionText => DisplayText;
 

src/EditorFeatures/Core/Implementation/IntelliSense/Completion/Presentation/Roslyn14CompletionSet.cs

@@ -140,10 +140,12 @@ private VSCompletion GetVSCompletion(CompletionItem item, string displayText = n
             VSCompletion value;
             if (!CompletionItemMap.TryGetValue(item, out value))
             {
-                value = new CustomCommitCompletion(CompletionPresenterSession, item, displayText);
+                value = new CustomCommitCompletion(CompletionPresenterSession, item);
                 CompletionItemMap.Add(item, value);
             }
 
+            value.DisplayText = displayText ?? item.DisplayText;
+
             return value;
         }