[lex.charset] Move reference to glyphs to appropriate place

The statement that glyphs are used to identify members of the
basic character set does not belong separating two sentences
introducing and then defining preprocessing tokens.

Also, we do not *exlusively* use glyphs for this purpose but
also directly call out Unicode code points too, so tone down
the phrasing to glyphs are *often* used to ...

Author: AlisdairM

source/lex.tex

@@ -317,6 +317,9 @@
 \pnum
 The \defnadj{basic}{character set} is a subset of the translation character set,
 consisting of 99 characters as specified in \tref{lex.charset.basic}.
+In this document,
+glyphs are often used to identify
+elements of the basic character set.
 \begin{note}
 Unicode short names are given only as a means to identifying the character;
 the numerical value has no other meaning in this context.
@@ -548,9 +551,6 @@
 \pnum
 A preprocessing token is the minimal lexical element of the language in translation
 phases 3 through 5.
-In this document,
-glyphs are used to identify
-elements of the basic character set\iref{lex.charset}.
 The categories of preprocessing token are: header names,
 placeholder tokens produced by preprocessing \tcode{import} and \tcode{module} directives
 (\grammarterm{import-keyword}, \grammarterm{module-keyword}, and \grammarterm{export-keyword}),