Cross-check lists of predefined LWLocks.

Both lwlocknames.txt and wait_event_names.txt contain a list of all
the predefined LWLocks, i.e., those with predefined positions
within MainLWLockArray.  It is easy to miss one or the other,
especially since the list in wait_event_names.txt omits the "Lock"
suffix from all the LWLock wait events.  This commit adds a cross-
check of these lists to the script that generates lwlocknames.h.
If the lists do not match exactly, building will fail.

Suggested-by: Robert Haas
Reviewed-by: Robert Haas, Michael Paquier, Bertrand Drouvot
Discussion: https://postgr.es/m/20240102173120.GA1061678%40nathanxps13

src/backend/utils/activity/wait_event_names.txt

@@ -276,6 +276,10 @@ Extension	"Waiting in an extension."
 # This class of wait events has its own set of C structure, so these are
 # only used for the documentation.
 #
+# NB: Predefined LWLocks (i.e., those declared in lwlocknames.txt) must be
+# listed in the top section of locks and must be listed in the same order as in
+# lwlocknames.txt.
+#
 
 Section: ClassName - WaitEventLWLock
 
@@ -326,6 +330,14 @@ NotifyQueueTail	"Waiting to update limit on <command>NOTIFY</command> message st
 WaitEventExtension	"Waiting to read or update custom wait events information for extensions."
 WALSummarizer	"Waiting to read or update WAL summarization state."
 
+#
+# END OF PREDEFINED LWLOCKS (DO NOT CHANGE THIS LINE)
+#
+# Predefined LWLocks (i.e., those declared in lwlocknames.txt) must be listed
+# in the section above and must be listed in the same order as in
+# lwlocknames.txt.  Other LWLocks must be listed in the section below.
+#
+
 XactBuffer	"Waiting for I/O on a transaction status SLRU buffer."
 CommitTsBuffer	"Waiting for I/O on a commit timestamp SLRU buffer."
 SubtransBuffer	"Waiting for I/O on a sub-transaction SLRU buffer."