This is straightforward as far as it goes. However, it does not
attempt to trap errors occurring during the execution of domain
CHECK constraints. Since those are general user-defined
expressions, the only way to do that would involve starting up a
subtransaction for each check. Of course the entire point of
the soft-errors feature is to not need subtransactions, so that
would be self-defeating. For now, we'll rely on the assumption
that domain checks are written to avoid throwing errors.
Discussion: https://postgr.es/m/1181028.1670635727@sss.pgh.pa.us
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