[lex.literal] Properly format table headings

Fixes ISO/CS comment (C++23 proof)

Author: jensmaurer

source/lex.tex

@@ -1466,8 +1466,8 @@
 \begin{floattable}{Character literals}{lex.ccon.literal}
 {l|l|l|l|l}
 \topline
-Encoding & Kind & Type & Associated char- & Example \\
-prefix & & & acter encoding & \\
+\lhdr{Encoding} & \chdr{Kind} & \chdr{Type} & \chdr{Associated char-} & \rhdr{Example} \\
+\lhdr{prefix} & \chdr{} & \chdr{} & \chdr{acter encoding} & \\
 \capsep
 none &
 \defnx{ordinary character literal}{literal!character!ordinary} &
@@ -1805,9 +1805,9 @@
 \begin{floattable}{String literals}{lex.string.literal}
 {llp{2.6cm}p{2.3cm}p{4.7cm}}
 \topline
-Encoding & Kind & Type & Associated & Examples \\
-prefix   &      &      & character  & \\
-         &      &      & encoding   & \\
+\lhdr{Enco-} & \chdr{Kind} & \chdr{Type} & \chdr{Associated} & \rhdr{Examples} \\
+\lhdr{ding}   & \chdr{} & \chdr{} & \chdr{character}  & \rhdr{} \\
+\lhdr{prefix}         & \chdr{} & \chdr{} & \chdr{encoding}   & \rhdr{} \\
 \capsep
 none &
 \defnx{ordinary string literal}{literal!string!ordinary} &