[lex.string] Fix excessive whitespace stretching by allowing a linebreak

in the middle of the interval "[E000, 10FFFF]".

Author: zygoloid

source/lex.tex

@@ -1786,7 +1786,7 @@
 \begin{note}
 Any \grammarterm{universal-character-name}{s} are required to
 correspond to a code point in the range
-$[0, \mathrm{D800})$ or $[\mathrm{E000}, \mathrm{10FFFF}]$ (hexadecimal)\iref{lex.charset}.
+$[0,$ $\mathrm{D800})$ or $[\mathrm{E000},$ $\mathrm{10FFFF}]$ (hexadecimal)\iref{lex.charset}.
 \end{note}
 The size of a narrow string literal is
 the total number of escape sequences and other characters, plus at least