Handle DisplayTextPrefix and DisplayTextSuffix on completion itmes

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

@@ -60,15 +60,27 @@ static LSP.CompletionItem CreateLSPCompletionItem(LSP.CompletionParams request,
             }
 
             static TCompletionItem CreateCompletionItem<TCompletionItem>(LSP.CompletionParams request, CompletionItem item) where TCompletionItem : LSP.CompletionItem, new()
-                => new TCompletionItem
+            {
+                var label = "";
+                if (item.DisplayTextPrefix != null)
+                {
+                    label += item.DisplayTextPrefix;
+                }
+                label += item.DisplayText;
+                if (item.DisplayTextSuffix != null)
                 {
-                    Label = item.DisplayText,
+                    label += item.DisplayTextSuffix;
+                }
+                return new TCompletionItem
+                {
+                    Label = label,
                     InsertText = item.Properties.ContainsKey("InsertionText") ? item.Properties["InsertionText"] : item.DisplayText,
                     SortText = item.SortText,
                     FilterText = item.FilterText,
                     Kind = GetCompletionKind(item.Tags),
                     Data = new CompletionResolveData { CompletionParams = request, DisplayText = item.DisplayText }
                 };
+            }
         }
 
         private static LSP.CompletionItemKind GetCompletionKind(ImmutableArray<string> tags)