Cleanup copy functions and move to base.h

include/fmt/compile.h

@@ -15,9 +15,9 @@
 FMT_BEGIN_NAMESPACE
 namespace detail {
 
-template <typename Char, typename InputIt>
-FMT_CONSTEXPR inline auto copy_str(InputIt begin, InputIt end,
-                                   counting_iterator it) -> counting_iterator {
+template <typename T, typename InputIt>
+FMT_CONSTEXPR inline auto copy(InputIt begin, InputIt end, counting_iterator it)
+    -> counting_iterator {
   return it + (end - begin);
 }
 
@@ -148,7 +148,7 @@ template <typename Char, typename T, int N> struct field {
     const T& arg = get_arg_checked<T, N>(args...);
     if constexpr (std::is_convertible_v<T, basic_string_view<Char>>) {
       auto s = basic_string_view<Char>(arg);
-      return copy_str<Char>(s.begin(), s.end(), out);
+      return copy<Char>(s.begin(), s.end(), out);
     }
     return write<Char>(out, arg);
   }