pgsql: common/jsonapi: support libpq as a client

common/jsonapi: support libpq as a client

Based on a patch by Michael Paquier.

For libpq, use PQExpBuffer instead of StringInfo. This requires us to
track allocation failures so that we can return JSON_OUT_OF_MEMORY as
needed rather than exit()ing.

Author: Jacob Champion <jacob(dot)champion(at)enterprisedb(dot)com>
Co-authored-by: Michael Paquier <michael(at)paquier(dot)xyz>
Co-authored-by: Daniel Gustafsson <daniel(at)yesql(dot)se>
Reviewed-by: Peter Eisentraut <peter(at)eisentraut(dot)org>
Discussion: https://www.postgresql.org/message-id/flat/d1b467a78e0e36ed85a09adf979d04cf124a9d4b(dot)camel(at)vmware(dot)com

Branch
------
master

Details
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https://git.postgresql.org/pg/commitdiff/0785d1b8b2fa27074eeb18a3ac1f2a0e76cb8339

Modified Files
--------------
src/common/Makefile | 23 +-
src/common/jsonapi.c | 473 +++++++++++++++------
src/common/meson.build | 35 +-
src/include/common/jsonapi.h | 18 +-
src/test/modules/test_json_parser/Makefile | 7 +-
src/test/modules/test_json_parser/meson.build | 12 +
.../t/001_test_json_parser_incremental.pl | 25 +-
src/test/modules/test_json_parser/t/002_inline.pl | 177 ++++----
.../test_json_parser/t/003_test_semantic.pl | 31 +-
9 files changed, 558 insertions(+), 243 deletions(-)