Reorganize logical replication worker disconnect code

Move the walrcv_disconnect() calls into the before_shmem_exit handler.
This makes sure the call is always made even during exit by signal, it
saves some duplicate code, and it makes the logic more similar to
walreceiver.c.

Author: Petr Jelinek <petr.jelinek@2ndquadrant.com>

src/backend/replication/logical/launcher.c

@@ -614,7 +614,13 @@ logicalrep_launcher_onexit(int code, Datum arg)
 static void
 logicalrep_worker_onexit(int code, Datum arg)
 {
+	/* Disconnect gracefully from the remote side. */
+	if (wrconn)
+		walrcv_disconnect(wrconn);
+
 	logicalrep_worker_detach();
+
+	ApplyLauncherWakeup();
 }
 
 /* SIGTERM: set flag to exit at next convenient time */

src/backend/replication/logical/tablesync.c

@@ -140,7 +140,6 @@ finish_sync_worker(void)
 	CommitTransactionCommand();
 
 	/* Stop gracefully */
-	walrcv_disconnect(wrconn);
 	proc_exit(0);
 }
 

src/backend/replication/logical/worker.c

@@ -1329,7 +1329,6 @@ reread_subscription(void)
 				   "stop because the subscription was removed",
 				   MySubscription->name)));
 
-		walrcv_disconnect(wrconn);
 		proc_exit(0);
 	}
 
@@ -1344,7 +1343,6 @@ reread_subscription(void)
 				   "stop because the subscription was disabled",
 				   MySubscription->name)));
 
-		walrcv_disconnect(wrconn);
 		proc_exit(0);
 	}
 
@@ -1359,7 +1357,6 @@ reread_subscription(void)
 				   "restart because the connection information was changed",
 				   MySubscription->name)));
 
-		walrcv_disconnect(wrconn);
 		proc_exit(0);
 	}
 
@@ -1374,7 +1371,6 @@ reread_subscription(void)
 				   "restart because subscription was renamed",
 				   MySubscription->name)));
 
-		walrcv_disconnect(wrconn);
 		proc_exit(0);
 	}
 
@@ -1392,7 +1388,6 @@ reread_subscription(void)
 				   "restart because the replication slot name was changed",
 				   MySubscription->name)));
 
-		walrcv_disconnect(wrconn);
 		proc_exit(0);
 	}
 
@@ -1407,7 +1402,6 @@ reread_subscription(void)
 				   "restart because subscription's publications were changed",
 				   MySubscription->name)));
 
-		walrcv_disconnect(wrconn);
 		proc_exit(0);
 	}
 
@@ -1610,8 +1604,6 @@ ApplyWorkerMain(Datum main_arg)
 	/* Run the main loop. */
 	LogicalRepApplyLoop(origin_startpos);
 
-	walrcv_disconnect(wrconn);
-
 	/* We should only get here if we received SIGTERM */
 	proc_exit(0);
 }