Add documentHighlight in clangd check for performance measurements.

clang-tools-extra/clangd/tool/Check.cpp

for (const auto &Tok : SpelledTokens) {
         }
       }
       unsigned Definitions = locateSymbolAt(*AST, Pos, &Index).size();
       vlog("    definition: {0}", Definitions);
 
       auto Hover = getHover(*AST, Pos, Style, &Index);
       vlog("    hover: {0}", Hover.hasValue());
 
+      unsigned DocHighlights = findDocumentHighlights(*AST, Pos).size();
+      vlog("    documentHighlight: {0}", DocHighlights);
+
       if (EnableCodeCompletion) {
         Position EndPos = offsetToPosition(Inputs.Contents, End);
         auto CC = codeComplete(File, EndPos, Preamble.get(), Inputs, CCOpts);
         vlog("    code completion: {0}",
              CC.Completions.empty() ? "<empty>" : CC.Completions[0].Name);
       }
     }
   }