refactor(string_view_base): directly call boost::hash_range

Since boostorg/core@92f6cfb in Boost.Core, we have been getting "error: use of undeclared identifier 'hash_value'" because hash_value is not part of the interface of core::string_view.

This commit implements the same strategy as previously used in Boost.Core to avoid breaking changes.

include/boost/url/grammar/string_view_base.hpp

@@ -20,6 +20,10 @@
 #include <utility>
 
 namespace boost {
+
+// forward declaration of boost::hash_range from ContainerHash
+template<class It> std::size_t hash_range( It, It );
+
 namespace urls {
 namespace grammar {
 
@@ -864,7 +868,7 @@ class string_view_base
     hash_value(
         string_view_base const& s) noexcept
     {
-        return hash_value(s.s_);
+        return boost::hash_range( s.s_.begin(), s.s_.end() );
     }
 
     /** Format a string to an output stream