Handle DisplayTextPrefix and DisplayTextSuffix on completion itmes

src/Features/LanguageServer/Protocol/Handler/Completion/CompletionHandler.cs

@@ -60,9 +60,20 @@ static LSP.CompletionItem CreateLSPCompletionItem(LSP.CompletionParams request,
             }
 
             static TCompletionItem CreateCompletionItem<TCompletionItem>(LSP.CompletionParams request, CompletionItem item) where TCompletionItem : LSP.CompletionItem, new()
-                => new TCompletionItem
             {
-                    Label = item.DisplayText,
+                var label = "";
+                if (item.DisplayTextPrefix != null)
+                {
+                    label += item.DisplayTextPrefix;
+                }
+                label += item.DisplayText;
+                if (item.DisplayTextSuffix != null)
+                {
+                    label += item.DisplayTextSuffix;
+                }
+                return new TCompletionItem
+                {
+                    Label = label,
                     InsertText = item.Properties.ContainsKey("InsertionText") ? item.Properties["InsertionText"] : item.DisplayText,
                     SortText = item.SortText,
                     FilterText = item.FilterText,
@@ -70,6 +81,7 @@ static TCompletionItem CreateCompletionItem<TCompletionItem>(LSP.CompletionParam
                     Data = new CompletionResolveData { CompletionParams = request, DisplayText = item.DisplayText }
                 };
             }
+        }
 
         private static LSP.CompletionItemKind GetCompletionKind(ImmutableArray<string> tags)
         {