[coro.generator.promise] Fix template parameters (#6009)

Some of the template parameters of `yield_value` were inconsistent,
and the synopsis contained an outright typo. This change uses `R2`
consistently since the parameter is a reference.

Author: MFHava

source/ranges.tex

@@ -15215,8 +15215,8 @@
         @\libconcept{constructible_from}@<remove_cvref_t<yielded>, const remove_reference_t<yielded>&>;
 
     template<class R2, class V2, class Alloc2, class Unused>
-      requires @\libconcept{same_as}@<typename generator<T2, V2, Alloc2>::yielded, yielded>
-        auto yield_value(ranges::elements_of<generator<T2, V2, Alloc2>&&, Unused> g) noexcept;
+      requires @\libconcept{same_as}@<typename generator<R2, V2, Alloc2>::yielded, yielded>
+        auto yield_value(ranges::elements_of<generator<R2, V2, Alloc2>&&, Unused> g) noexcept;
 
     template<ranges::@\libconcept{input_range}@ R, class Alloc>
       requires @\libconcept{convertible_to}@<ranges::range_reference_t<R>, yielded>
@@ -15341,9 +15341,9 @@
 
 \indexlibrarymember{yield_value}{generator::promise_type}%
 \begin{itemdecl}
-template<class T2, class V2, class Alloc2, class Unused>
-  requires @\libconcept{same_as}@<typename generator<T2, V2, Alloc2>::yielded, yielded>
-  auto yield_value(ranges::elements_of<generator<T2, V2, Alloc2>&&, Unused> g) noexcept;
+template<class R2, class V2, class Alloc2, class Unused>
+  requires @\libconcept{same_as}@<typename generator<R2, V2, Alloc2>::yielded, yielded>
+  auto yield_value(ranges::elements_of<generator<R2, V2, Alloc2>&&, Unused> g) noexcept;
 \end{itemdecl}
 
 \begin{itemdescr}