Specify includeDocumentationComments parameter in C# cref completion

src/Features/CSharp/Portable/Completion/CompletionProviders/CrefCompletionProvider.cs

@@ -56,7 +56,7 @@ public override async Task ProduceCompletionListAsync(CompletionListContext cont
                 return;
             }
 
-            var token = tree.FindTokenOnLeftOfPosition(position, cancellationToken)
+            var token = tree.FindTokenOnLeftOfPosition(position, cancellationToken, includeDocumentationComments: true)
                             .GetPreviousTokenIfTouchingWord(position);
 
             // To get a Speculative SemanticModel (which is much faster), we need to