Missing dependency tracking for TableFunc nodes

I happened to notice that find_expr_references_walker has not
been taught anything about TableFunc nodes, which means it will
miss the type and collation OIDs embedded in such a node.

This can be demonstrated to be a problem by the attached script,
which will end up with a "cache lookup failed for type NNNNN"
error because we allow dropping a type the XMLTABLE construct
references.

This isn't hard to fix, as per the attached patch, but it makes
me nervous. I wonder what other dependencies we might be missing.

Would it be a good idea to move find_expr_references_walker to
nodeFuncs.c, in hopes of making it more visible to people adding
new node types? We could decouple it from the specific use-case
of recordDependencyOnExpr by having it call a callback function
for each identified OID; although maybe there's no point in that,
since I'm not sure there are any other use-cases.

Another thought is that maybe the code could be automatically
generated, as Andres has been threatening to do with respect
to the other stuff in backend/nodes/.

In practice, this bug is probably not a huge problem, because a
view that involves a column of type X will likely have some other
dependencies on X. I had to tweak the example view a bit to get
it to not have any other dependencies on "seg". So I'm not feeling
that this is a stop-ship problem for today's releases --- I'll plan
on installing the fix after the releases are tagged.

regards, tom lane