We have a not-terribly-thoroughly-enforced-yet project policy that internal
errors with SQLSTATE XX000 (ie, plain elog) should not be triggerable from
SQL.  record_in, domain_in, and PL validator functions all failed to meet
this standard, because they threw plain elog("cache lookup failed for XXX")
errors on bad OIDs, and those are all invokable from SQL.

For record_in, the best fix is to upgrade typcache.c (lookup_type_cache)
to throw a user-facing error for this case.  That seems consistent because
it was more than halfway there already, having user-facing errors for shell
types and non-composite types.  Having done that, tweak domain_in to rely
on the typcache to throw an appropriate error.  (This costs little because
InitDomainConstraintRef would fetch the typcache entry anyway.)

For the PL validator functions, we already have a single choke point at
CheckFunctionValidatorAccess, so just fix its error to be user-facing.

Dilip Kumar, reviewed by Haribabu Kommi

Discussion: <87wpxfygg9.fsf@credativ.de>