CWG2639 new-lines after phase 1

Fixes NB US 030 (C++23 CD).

Author: burblebee

source/lex.tex

@@ -82,12 +82,18 @@
 then it shall be a well-formed UTF-8 code unit sequence and
 it is decoded to produce a sequence of UCS scalar values
 that constitutes the sequence of elements of the translation character set.
+In the resulting sequence,
+each pair of characters in the input sequence consisting of
+\unicode{000d}{carriage return} followed by \unicode{000a}{line feed},
+as well as each
+\unicode{000d}{carriage return} not immediately followed by a \unicode{000a}{line feed},
+is replaced by a single new-line character.
 
 For any other kind of input file supported by the implementation,
 characters are mapped, in an
 \impldef{mapping physical source file characters to translation character set} manner,
-to a sequence of translation character set elements\iref{lex.charset}
-(introducing new-line characters for end-of-line indicators).
+to a sequence of translation character set elements\iref{lex.charset},
+representing end-of-line indicators as new-line characters.
 
 \item
 \indextext{line splicing}%