[basic.link], [expr.ref] Harmonize font for tuple representing direct base class relationship

Fixes NB US 1-405 (C++26 CD).

Author: eisenwave

source/basic.tex

@@ -3264,7 +3264,7 @@
 \item
 an entity, value, or object that is TU-local,
 \item
-a direct base class relationship (\tcode{D}, \tcode{B})\iref{class.derived.general}
+a direct base class relationship $(D, B)$\iref{class.derived.general}
 for which either \tcode{D} or \tcode{B} is TU-local, or
 \item
 a data member description ($T$, $N$, $A$, $W$, $\mathit{NUA}$)\iref{class.mem.general}

source/expressions.tex

@@ -4219,10 +4219,10 @@
 
 \pnum
 If \tcode{E2} is a \grammarterm{splice-expression},
-then let \tcode{T1} be the type of \tcode{E1}.
+then let $\mathit{T1}$ be the type of \tcode{E1}.
 \tcode{E2} shall designate either
-a member of \tcode{T1} or
-a direct base class relationship $(\tcode{T1}, \tcode{B})$.
+a member of $\mathit{T1}$ or
+a direct base class relationship $(\mathit{T1}, B)$.
 
 \pnum
 If \tcode{E2} designates a bit-field, \tcode{E1.E2} is a bit-field. The