pgsql: Convert built-in SQL-language functions to SQL-standard-body sty

Convert built-in SQL-language functions to SQL-standard-body style.

Adopt the new pre-parsed representation for all built-in and
information_schema SQL-language functions, except for a small
number that can't presently be converted because they have
polymorphic arguments.

This eliminates residual hazards around search-path safety of
these functions, and might provide some small performance benefits
by reducing parsing costs.  It seems useful also to provide more
test coverage for the SQL-standard-body feature.

Discussion: https://postgr.es/m/3956760.1618529139@sss.pgh.pa.us

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/767982e36298be4da44a063e36261e9cfdc0bf49

Modified Files
--------------
src/backend/catalog/information_schema.sql |  48 ++--
src/backend/catalog/system_functions.sql   | 350 ++++++++++++++++++++++++++---
src/include/catalog/catversion.h           |   2 +-
src/include/catalog/pg_proc.dat            | 115 +++++-----
4 files changed, 402 insertions(+), 113 deletions(-)