Go: refactor (#16602)

### Summary

1. update doc
2. refactor route code

---------

Signed-off-by: Jin Hai <haijin.chn@gmail.com>

internal/binding/cpp/util/strutil.h

@@ -0,0 +1,21 @@
+// Copyright 2016 The RE2 Authors.  All Rights Reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+#ifndef UTIL_STRUTIL_H_
+#define UTIL_STRUTIL_H_
+
+#include <string>
+
+#include "re2/stringpiece.h"
+#include "util/util.h"
+
+namespace re2 {
+
+std::string CEscape(const StringPiece &src);
+void PrefixSuccessor(std::string *prefix);
+std::string StringPrintf(const char *format, ...);
+
+} // namespace re2
+
+#endif // UTIL_STRUTIL_H_