[exec.par.scheduler] Fix extent of definitions

As per P2079R10.

Author: tkoeppe

source/exec.tex

@@ -8288,7 +8288,7 @@
 
 \pnum
 Let \tcode{rcvr} be a receiver.
-A \defn{proxy} for \tcode{rcvr} with base \tcode{B} is
+A \defnx{proxy for \tcode{rcvr} with base \tcode{B}}{proxy} is
 an lvalue \tcode{r} of type \tcode{B} such that:
 \begin{itemize}
 \item
@@ -8314,17 +8314,17 @@
 \end{note}
 
 \pnum
-A \defnadj{bulk chunked}{proxy} for \tcode{rcvr}
-with callable \tcode{f} and arguments \tcode{args}
+A \defnx{bulk chunked proxy for \tcode{rcvr}
+with callable \tcode{f} and arguments \tcode{args}}{proxy!bulk chunked}
 is a proxy \tcode{r} for \tcode{rcvr}
 with base \tcode{system_context_replaceability::bulk_item_receiver_proxy}
 such that
 \tcode{r.execute(i, j)} for indices \tcode{i} and \tcode{j}
 has effects equivalent to \tcode{f(i, j, args...)}.
 
 \pnum
-A \defnadj{bulk unchunked}{proxy} for \tcode{rcvr}
-with callable \tcode{f} and arguments \tcode{args}
+A \defnx{bulk unchunked proxy for \tcode{rcvr}
+with callable \tcode{f} and arguments \tcode{args}}{proxy!bulk unchunked}
 is a proxy \tcode{r} for \tcode{rcvr}
 with base \tcode{system_context_replaceability::bulk_item_receiver_proxy}
 such that