Fix O(N^2) performance issue in pg_publication_tables view.

The original coding of this view relied on a correlated IN sub-query.
Our planner is not very bright about correlated sub-queries, and even
if it were, there's no way for it to know that the output of
pg_get_publication_tables() is duplicate-free, making the de-duplicating
semantics of IN unnecessary.  Hence, rewrite as a LATERAL sub-query.
This provides circa 100X speedup for me with a few hundred published
tables (the whole regression database), and things would degrade as
roughly O(published_relations * all_relations) beyond that.

Because the rules.out expected output changes, force a catversion bump.
Ordinarily we might not want to do that post-beta1; but we already know
we'll be doing a catversion bump before beta2 to fix pg_statistic_ext
issues, so it's pretty much free to fix it now instead of waiting for v13.

Per report and fix suggestion from PegoraroF10.

Discussion: https://postgr.es/m/1551385426763-0.post@n3.nabble.com

src/test/regress/expected/rules.out

@@ -1441,10 +1441,10 @@ pg_publication_tables| SELECT p.pubname,
     n.nspname AS schemaname,
     c.relname AS tablename
    FROM pg_publication p,
+    LATERAL pg_get_publication_tables((p.pubname)::text) gpt(relid),
     (pg_class c
      JOIN pg_namespace n ON ((n.oid = c.relnamespace)))
-  WHERE (c.oid IN ( SELECT pg_get_publication_tables.relid
-           FROM pg_get_publication_tables((p.pubname)::text) pg_get_publication_tables(relid)));
+  WHERE (c.oid = gpt.relid);
 pg_replication_origin_status| SELECT pg_show_replication_origin_status.local_id,
     pg_show_replication_origin_status.external_id,
     pg_show_replication_origin_status.remote_lsn,