Add a couple of regression test cases related to array subscripting.

Exercise some error cases that were never reached in the existing
regression tests.  This is partly for code-coverage reasons, and
partly to memorialize the current behavior in advance of planned
changes for generic subscripting.

Also, I noticed that type_sanity's check to verify that all standard
types have array types was never extended when we added arrays for
all system catalog rowtypes (f7f70d5e2), nor when we added arrays
over domain types (c12d570fa).  So do that.  Also, since the query's
expected output isn't empty, it seems like a good idea to add an
ORDER BY to make sure the result stays stable.

src/test/regress/sql/arrays.sql

@@ -34,6 +34,9 @@ INSERT INTO arrtest (a, b[1:2][1:2], c, d, e, f, g)
 INSERT INTO arrtest (a, b[1:2], c, d[1:2])
    VALUES ('{}', '{3,4}', '{foo,bar}', '{bar,foo}');
 
+INSERT INTO arrtest (b[2]) VALUES(now());  -- error, type mismatch
+
+INSERT INTO arrtest (b[1:2]) VALUES(now());  -- error, type mismatch
 
 SELECT * FROM arrtest;
 
@@ -122,6 +125,8 @@ UPDATE arrtest
 UPDATE arrtest
   SET c[1:NULL] = '{"can''t assign"}'
   WHERE array_dims(c) is not null;
+-- Un-subscriptable type
+SELECT (now())[1];
 
 -- test slices with empty lower and/or upper index
 CREATE TEMP TABLE arrtest_s (