pgsql: Avoid producing over-length specific_name outputs ininformation

Avoid producing over-length specific_name outputs in information_schema.

information_schema output columns that are declared as being type
sql_identifier are supposed to conform to the implementation's rules
for valid identifiers, in particular the identifier length limit.
Several places potentially violated this limit by concatenating a
function's name and OID.  (The OID is added to ensure name uniqueness
within a schema, since the spec doesn't expect function name overloading.)

Simply truncating the concatenation result to fit in "name" won't do,
since losing part of the OID might wind up giving non-unique results.
Instead, let's truncate the function name as necessary.

The most practical way to do that is to do it in a C function; the
information_schema.sql script doesn't have easy access to the value
of NAMEDATALEN, nor does it have an easy way to truncate on the basis
of resulting byte-length rather than number of characters.

(There are still a couple of places that cast concatenation results to
sql_identifier, but as far as I can see they are guaranteed not to produce
over-length strings, at least with the normal value of NAMEDATALEN.)

Discussion: https://postgr.es/m/23817.1545283477@sss.pgh.pa.us

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/5bbee34d9f2e6097247ace3ebe1dde1f6aa80287

Modified Files
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src/backend/catalog/information_schema.sql | 20 +++++++++--------
src/backend/utils/adt/name.c               | 35 ++++++++++++++++++++++++++++++
src/include/catalog/catversion.h           |  2 +-
src/include/catalog/pg_proc.dat            |  4 ++++
4 files changed, 51 insertions(+), 10 deletions(-)