[basic.types] Add index entries for trivial class etc.

Also reformat text to avoid line breaks in the middle of a grammatical
clause.

source/basic.tex

@@ -3760,17 +3760,19 @@
 a function type, not a reference type, and not \cv{}~\tcode{void}.
 
 \pnum
-Arithmetic types\iref{basic.fundamental}, enumeration types, pointer
-types, pointer-to-member types\iref{basic.compound},
+\indextext{class!trivial}
+\indextext{class!trivially copyable}
+\indextext{class!standard-layout}
+Arithmetic types\iref{basic.fundamental}, enumeration types,
+pointer types, pointer-to-member types\iref{basic.compound},
 \tcode{std::nullptr_t},
 and
 cv-qualified\iref{basic.type.qualifier} versions of these
 types are collectively called
 \defnx{scalar types}{scalar type}.
-Cv-unqualified scalar types, trivially copyable class types\iref{class}, arrays of
-such types, and cv-qualified versions of these
-types are collectively called \defn{trivially
-copyable types}.
+Cv-unqualified scalar types, trivially copyable class types\iref{class},
+arrays of such types, and cv-qualified versions of these
+types are collectively called \defn{trivially copyable types}.
 Scalar types, trivial class types\iref{class},
 arrays of such types and cv-qualified versions of these
 types are collectively called