[func.wrap.ref.class] Fix use of template parameter name "ArgTypes".

Also use a codeblock to make the code presentation a bit tidier,
and add descriptive nouns before symbolic references.

Author: tkoeppe

source/utilities.tex

@@ -14959,10 +14959,10 @@
 
   private:
     template<class... T>
-      static constexpr bool @\exposidnc{is-invocable-using}@ = @\seebelownc@;     // \expos
+      static constexpr bool @\exposidnc{is-invocable-using}@ = @\seebelownc@;             // \expos
 
-    R (*@\exposidnc{thunk-ptr}@)(@\exposidnc{BoundEntityType}@, Args&&...) noexcept(@\placeholdernc{noex}@);  // \expos
-    @\exposidnc{BoundEntityType}@ @\exposidnc{bound-entity}@;                               // \expos
+    R (*@\exposidnc{thunk-ptr}@)(@\exposidnc{BoundEntityType}@, ArgTypes&&...) noexcept(@\placeholdernc{noex}@);      // \expos
+    @\exposidnc{BoundEntityType}@ @\exposidnc{bound-entity}@;                                       // \expos
   };
 
   // \ref{func.wrap.ref.deduct}, deduction guides
@@ -14980,7 +14980,7 @@
 \tcode{function_ref<R(Args...) \cv{} noexcept(\placeholder{noex})>}
 stores a pointer to function \exposid{thunk-ptr} and
 an object \exposid{bound-entity}.
-\exposid{bound-entity} has
+The object \exposid{bound-entity} has
 an unspecified trivially copyable type \exposid{BoundEntityType}, that
 models \libconcept{copyable} and
 is capable of storing a pointer to object value or a pointer to function value.
@@ -14993,10 +14993,12 @@
 that models \libconcept{copyable}.
 
 \pnum
-Within \ref{func.wrap.ref},
+Within subclause~\ref{func.wrap.ref},
 \tcode{\placeholder{call-args}} is an argument pack with elements such that
-\tcode{decltype((\placeholder{call-args}\linebreak{}))...} denote
-\tcode{Args\&\&...} respectively.
+\begin{codeblock}
+decltype((@\placeholder{call-args}@))...
+\end{codeblock}
+denote \tcode{ArgTypes\&\&...} respectively.
 
 \rSec4[func.wrap.ref.ctor]{Constructors and assignment operators}