Replace boost::string_ref with std::string_view

include/util/guidance/name_announcements.hpp

@@ -70,7 +70,10 @@ template <typename StringView> inline auto decompose(const StringView &lhs, cons
     const auto trim = [](StringView view) {
         // we compare suffixes based on this value, it might break UTF chars, but as long as we are
         // consistent in handling, we do not create bad results
-        std::string str = boost::to_lower_copy(view.to_string());
+        std::string str(view);
+        std::transform(str.begin(), str.end(), str.begin(), 
+                   [](unsigned char c){ return std::tolower(c); } // correct
+        );
         auto front = str.find_first_not_of(' ');
 
         if (front == std::string::npos)

include/util/string_view.hpp

@@ -2,14 +2,14 @@
 #define OSRM_STRING_VIEW_HPP
 
 #include <boost/functional/hash.hpp>
-#include <boost/utility/string_ref.hpp>
+#include <string_view>
 
 namespace osrm
 {
 namespace util
 {
 // Convenience typedef: boost::string_ref, boost::string_view or C++17's string_view
-using StringView = boost::string_ref;
+using StringView = std::string_view;
 
 } // namespace util
 } // namespace osrm