[format.range.fmtdef] Add "exposition only" comments

Author: tkoeppe

source/utilities.tex

@@ -15971,11 +15971,11 @@
 \begin{codeblock}
 namespace std {
   template<ranges::@\libconcept{input_range}@ R, class charT>
-  struct @\exposid{range-default-formatter}@<range_format::sequence, R, charT> {
+  struct @\exposidnc{range-default-formatter}@<range_format::sequence, R, charT> {    // \expos
   private:
-    using @\exposid{maybe-const-r}@ = @\exposid{fmt-maybe-const}@<R, charT>;
+    using @\exposid{maybe-const-r}@ = @\exposidnc{fmt-maybe-const}@<R, charT>;                    // \expos
     range_formatter<remove_cvref_t<ranges::range_reference_t<@\exposid{maybe-const-r}@>>,
-                    charT> @\exposid{underlying_}@;       // \expos
+                    charT> @\exposidnc{underlying_}@;                                 // \expos
 
   public:
     constexpr void set_separator(basic_string_view<charT> sep);