[range.join.iterator] Add missing \exposid

Author: lprv

source/ranges.tex

@@ -6838,7 +6838,7 @@
 \exposid{Base} models \libconcept{forward_range}, and
 \tcode{range_reference_t<\exposid{Base}>} models \libconcept{forward_range}.
 In that case,
-\tcode{iterator::iter\-ator_category} is defined as follows:
+\tcode{\exposid{iterator}::iter\-ator_category} is defined as follows:
 \begin{itemize}
 \item Let \placeholder{OUTERC} denote
   \tcode{iterator_traits<iterator_t<\exposid{Base}>>::iterator_category}, and
@@ -6858,7 +6858,7 @@
 \end{itemize}
 
 \pnum
-\tcode{iterator::difference_type} denotes the type:
+\tcode{\exposid{iterator}::difference_type} denotes the type:
 \begin{codeblock}
 common_type_t<
   range_difference_t<@\exposid{Base}@>,