Convert range_in and multirange_in to report errors softly.
This is mostly straightforward, except that if the range type
has a canonical function, that might throw an error during range
input. (Such errors probably only occur for edge cases: in the
in-core canonical functions, it happens only if a bound has the
maximum valid value for the underlying type.) Hence, this patch
extends the soft-error regime to allow canonical functions to
return errors softly as well. Extensions implementing range
canonical functions will need modification anyway because of the
API change for range_serialize(); while at it, they might want
to do something similar to what's been done here in the in-core
canonical functions.
Discussion: https://postgr.es/m/
3284599.
1671075185@sss.pgh.pa.us