Since 7c079d74, partition bounds are able to use generalized expression
syntax when processed, treating "minvalue" and "maxvalue" as specific
cases as they get passed down for transformation as a column references.

The checks for infinite bounds in range expressions have been lax
though, causing crashes when trying to use column reference names with
more than one field.  Here is an example causing a crash:
CREATE TABLE list_parted (a int) PARTITION BY LIST (a);
CREATE TABLE part_list_crash PARTITION OF list_parted
  FOR VALUES IN (somename.somename);

Note that the creation of the second relation should fail as partition
bounds cannot have column references in their expressions, so when
finding an expression which does not match the expected infinite bounds,
then this commit lets the generic transformation machinery check after
it.  The error message generated in this case references as well a
missing RTE, which is confusing.  This problem will be treated
separately as it impacts as well default expressions for some time, and
for now only the cases where a crash can happen are fixed.

While on it, extend the set of regression tests in place for list
partition bounds and add an extra set for range partition bounds.

Reported-by: Alexander Lakhin
Author: Michael Paquier
Reviewed-by: Amit Langote
Discussion: https://postgr.es/m/15668-0377b1981aa1a393@postgresql.org