[text.encoding.overview] Add cross-reference text_encoding​::​aliases_view (#7476)

Author: hewillk

source/text.tex

@@ -5043,6 +5043,7 @@
     constexpr id mib() const noexcept;
     constexpr const char* name() const noexcept;
 
+    // \ref{text.encoding.aliases}, class \tcode{text_encoding::aliases_view}
     struct aliases_view;
     constexpr aliases_view aliases() const noexcept;