Check for more Unicode functions during upgrade.

When checking for expression indexes that may be affected by a Unicode
update during upgrade, check for a few more functions. Specifically,
check for documented regexp functions, as well as the new CASEFOLD()
function.

Also, fully-qualify references to pg_catalog.text and
pg_catalog.regtype.

Discussion: https://postgr.es/m/399b656a3abb0c9283538a040f72199c0601525c.camel@j-davis.com
Backpatch-through: 18

src/bin/pg_upgrade/check.c

@@ -1971,14 +1971,19 @@ check_for_unicode_update(ClusterInfo *cluster)
 		"  SELECT oper.oid, oper.oprcode, collid FROM pg_operator oper, collations "
 		"  WHERE oprname IN ('~', '~*', '!~', '!~*', '~~*', '!~~*') AND "
 		"        oprnamespace='pg_catalog'::regnamespace AND "
-		"        oprright='text'::regtype "
+		"        oprright='pg_catalog.text'::pg_catalog.regtype "
 		"), "
 	/* functions that use the input collation for character semantics */
 		"coll_functions(procid, collid) AS ( "
 		"  SELECT proc.oid, collid FROM pg_proc proc, collations "
-		"  WHERE proname IN ('lower','initcap','upper') AND "
-		"        pronamespace='pg_catalog'::regnamespace AND "
-		"        proargtypes[0] = 'text'::regtype "
+		"  WHERE pronamespace='pg_catalog'::regnamespace AND "
+		"        ((proname IN ('lower','initcap','upper','casefold') AND "
+		"          pronargs = 1 AND "
+		"          proargtypes[0] = 'pg_catalog.text'::pg_catalog.regtype) OR "
+		"         (proname = 'substring' AND pronargs = 2 AND "
+		"          proargtypes[0] = 'pg_catalog.text'::pg_catalog.regtype AND "
+		"          proargtypes[1] = 'pg_catalog.text'::pg_catalog.regtype) OR "
+		"         proname LIKE 'regexp_%') "
 	/* include functions behind the operators listed above */
 		"  UNION "
 		"  SELECT procid, collid FROM coll_operators "