[exec.run.loop.general] Add \exposid for run-loop-opstate-base (#7773)

Author: hewillk

source/exec.tex

@@ -5173,7 +5173,7 @@
     struct @\exposid{run-loop-opstate-base}@ {                              // \expos
       virtual void @\exposid{execute}@() = 0;                               // \expos
       run_loop* @\exposid{loop}@;                                           // \expos
-      run-loop-opstate-base* @\exposid{next}@;                              // \expos
+      @\exposid{run-loop-opstate-base}@* @\exposid{next}@;                              // \expos
     };
     template<class Rcvr>
       using @\exposid{run-loop-opstate}@ = @\unspec@;                     // \expos