Fix WITHOUT OVERLAPS' interaction with domains.

Fix WITHOUT OVERLAPS' interaction with domains.

UNIQUE/PRIMARY KEY ... WITHOUT OVERLAPS requires the no-overlap
column to be a range or multirange, but it should allow a domain
over such a type too.  This requires minor adjustments in both
the parser and executor.

In passing, fix a nearby break-instead-of-continue thinko in
transformIndexConstraint.  This had the effect of disabling
parse-time validation of the no-overlap column's type in the context
of ALTER TABLE ADD CONSTRAINT, if it follows a dropped column.
We'd still complain appropriately at runtime though.

Author: Jian He <jian.universality@gmail.com>
Reviewed-by: Paul A Jungwirth <pj@illuminatedcomputing.com>
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/CACJufxGoAmN_0iJ=hjTG0vGpOSOyy-vYyfE+-q0AWxrq2_p5XQ@mail.gmail.com
Backpatch-through: 18