Expose the "*VALUES*" alias that we generate for a stand-alone VALUES list.

We were trying to make that strictly an internal implementation detail,
but it turns out that it's exposed anyway when dumping a view defined
like
	CREATE VIEW test_view AS VALUES (1), (2), (3) ORDER BY 1;
This comes out as
	CREATE VIEW ... ORDER BY "*VALUES*".column1;
which fails to parse when reloading the dump.

Hacking ruleutils.c to suppress the column qualification looks like it'd
be a risky business, so instead promote the RTE alias to full-fledged
usability.

Per bug #6049 from Dylan Adams.  Back-patch to all supported branches.