[const.iterators.{alias,iterators}] Add "exposition only" comments

Suggested by CD review feedback.

Author: tkoeppe

source/iterators.tex

@@ -4175,12 +4175,12 @@
 
 \begin{itemdecl}
 template<@\libconcept{indirectly_readable}@ It>
-  using iter_const_reference_t = common_reference_t<const iter_value_t<It>&&,
-                                                    iter_reference_t<It>>;
+  using iter_const_reference_t =
+    common_reference_t<const iter_value_t<It>&&, iter_reference_t<It>>;
 
 template<class It>
-  concept @\defexposconcept{constant-iterator}@ = @\libconcept{input_iterator}@<It> &&
-                              @\libconcept{same_as}@<iter_const_reference_t<It>, iter_reference_t<It>>;
+  concept @\defexposconcept{constant-iterator}@ =                                                   // \expos
+    @\libconcept{input_iterator}@<It> && @\libconcept{same_as}@<iter_const_reference_t<It>, iter_reference_t<It>>;
 
 template<@\libconcept{input_iterator}@ I>
   using @\libglobal{const_iterator}@ = @\seebelow@;
@@ -4214,8 +4214,8 @@
 
   template<@\libconcept{input_iterator}@ Iterator>
   class @\libglobal{basic_const_iterator}@ {
-    Iterator @\exposid{current_}@ = Iterator();
-    using @\exposid{reference}@ = iter_const_reference_t<Iterator>;         // \expos
+    Iterator @\exposidnc{current_}@ = Iterator();                             // \expos
+    using @\exposidnc{reference}@ = iter_const_reference_t<Iterator>;         // \expos
 
   public:
     using iterator_concept = @\seebelow@;