pgsql: Add infrastructure for pg_get_*_ddl functions

Add infrastructure for pg_get_*_ddl functions

Add parse_ddl_options(), append_ddl_option(), and append_guc_value()
helper functions in a new ddlutils.c file that provide common option
parsing and output formatting for the pg_get_*_ddl family of functions
which will follow in later patches.  These accept VARIADIC text
arguments as alternating name/value pairs.

Callers declare an array of DdlOption descriptors specifying the
accepted option names and their types (boolean, text, or integer).
parse_ddl_options() matches each supplied pair against the array,
validates the value, and fills in the result fields.  This
descriptor-based scheme is based on an idea from Euler Taveira.

This is placed in a new ddlutils.c file which will contain the
pg_get_*_ddl functions.

Author: Akshay Joshi <akshay.joshi@enterprisedb.com>
Co-authored-by: Andrew Dunstan <andrew@dunslane.net>
Co-authored-by: Euler Taveira <euler@eulerto.com>
Discussion: https://postgr.es/m/CAKWEB6rmnmGKUA87Zmq-s=b3Scsnj02C0kObQjnbL2ajfPWGEw@mail.gmail.com
Discussion: https://postgr.es/m/4c5f895e-3281-48f8-b943-9228b7da6471@gmail.com
Discussion: https://postgr.es/m/CANxoLDc6FHBYJvcgOnZyS+jF0NUo3Lq_83-rttBuJgs9id_UDg@mail.gmail.com
Discussion: https://postgr.es/m/e247c261-e3fb-4810-81e0-a65893170e94@dunslane.net

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/4881981f92024e4db6249bd3dc96a3859638a665

Modified Files
--------------
src/backend/utils/adt/Makefile    |   1 +
src/backend/utils/adt/ddlutils.c  | 275 ++++++++++++++++++++++++++++++++++++++
src/backend/utils/adt/meson.build |   1 +
src/tools/pgindent/typedefs.list  |   4 +-
4 files changed, 280 insertions(+), 1 deletion(-)