Ranges wide strings support (#2236)

* Ranges copy wchar_t

* arg_join formatter not working for wide strings

* Added ranges wide string tests

Co-authored-by: Cristi <cristi@emailaddressmanager.com>

include/fmt/format.h

@@ -3720,7 +3720,7 @@ struct formatter<arg_join<It, Sentinel, Char>, Char> {
  private:
   using value_type = typename std::iterator_traits<It>::value_type;
   using formatter_type =
-      conditional_t<has_formatter<value_type, format_context>::value,
+      conditional_t<has_formatter<value_type, buffer_context<Char>>::value,
                     formatter<value_type, Char>,
                     detail::fallback_formatter<value_type, Char>>;