[iostream.forward.overview] Add missing mentions of spanbuf and spanstreams

A follows up to P0448R4.

Author: frederick-vs-ja

source/iostreams.tex

@@ -363,17 +363,19 @@
 serves as a base class for class templates
 \tcode{basic_stringbuf},
 \tcode{basic_filebuf},
+\tcode{basic_syncbuf},
 and
-\tcode{basic_syncbuf}.
+\tcode{basic_spanbuf}.
 
 \pnum
 The
 class template specialization
 \tcode{basic_istream<charT, traits>}
 serves as a base class for class templates
-\tcode{basic_istringstream}
+\tcode{basic_istringstream},
+\tcode{basic_ifstream},
 and
-\tcode{basic_ifstream}.
+\tcode{basic_ispanstream}.
 
 \pnum
 The
@@ -382,17 +384,19 @@
 serves as a base class for class templates
 \tcode{basic_ostringstream},
 \tcode{basic_ofstream},
+\tcode{basic_osyncstream},
 and
-\tcode{basic_osyncstream}.
+\tcode{basic_ospanstream}.
 
 \pnum
 The
 class template specialization
 \tcode{basic_iostream<charT, traits>}
 serves as a base class for class templates
-\tcode{basic_stringstream}
+\tcode{basic_stringstream},
+\tcode{basic_fstream},
 and
-\tcode{basic_fstream}.
+\tcode{basic_spanstream}.
 
 \pnum
 \begin{note}