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>>;
 

include/fmt/ranges.h

@@ -67,6 +67,12 @@ OutputIterator copy(char ch, OutputIterator out) {
   return out;
 }
 
+template <typename OutputIterator>
+OutputIterator copy(wchar_t ch, OutputIterator out) {
+  *out++ = ch;
+  return out;
+}
+
 /// Return true value if T has std::string interface, like std::string_view.
 template <typename T> class is_like_std_string {
   template <typename U>