[execution.syn, task.promise] Move class definitions to synopsis

The definitions of with_error and change_coroutine_scheduler are now
in the main <execution> synopsis. They have no further description.

Author: dietmarkuehl

source/exec.tex

@@ -745,11 +745,23 @@
   // \ref{exec.task.scheduler}
   class @\libglobal{task_scheduler}@;
 
-  // \ref{exec.task}
   template<class E>
-    struct @\libglobal{with_error}@;
+  struct @\libglobal{with_error}@ {
+    using type = remove_cvref_t<E>;
+    type error;
+  };
+  template<class E>
+    with_error(E) -> with_error<E>;
+
   template<@\libconcept{scheduler}@ Sch>
-    struct @\libglobal{change_coroutine_scheduler}@;
+  struct change_coroutine_scheduler {
+    using type = remove_cvref_t<Sch>;
+    type scheduler;
+  };
+  template<@\libconcept{scheduler}@ Sch>
+    change_coroutine_scheduler(Sch) -> change_coroutine_scheduler<Sch>;
+
+  // \ref{exec.task}
   template<class T, class Environment>
     class @\libglobal{task}@;
 }
@@ -7447,22 +7459,6 @@
 
 \begin{codeblock}
 namespace std::execution {
-  template<class E>
-  struct @\libglobal{with_error}@ {
-    using type = remove_cvref_t<E>;
-    type error;
-  };
-  template<class E>
-    with_error(E) -> with_error<E>;
-
-  template<@\libconcept{scheduler}@ Sch>
-  struct change_coroutine_scheduler {
-    using type = remove_cvref_t<Sch>;
-    type scheduler;
-  };
-  template<@\libconcept{scheduler}@ Sch>
-    change_coroutine_scheduler(Sch) -> change_coroutine_scheduler<Sch>;
-
   template<class T, class Environment>
   class task<T, Environment>::promise_type {
   public: