[range.elements.iterator] Avoid "defining" typedef-names

Use "declare" instead.

Author: frederick-vs-ja

source/ranges.tex

@@ -10376,7 +10376,7 @@
 \end{itemize}
 
 \pnum
-The member \grammarterm{typedef-name} \tcode{iterator_category} is defined
+The member \grammarterm{typedef-name} \tcode{iterator_category} is declared
 if and only if \exposid{Base} models \libconcept{forward_range}.
 In that case, \tcode{iterator_category} is defined as follows:
 Let \tcode{C} denote the type