pgsql: Adjust pg_parse_json() so that it does not directly ereport().

Adjust pg_parse_json() so that it does not directly ereport().

Instead, it now returns a value indicating either success or the
type of error which occurred. The old behavior is still available
by calling pg_parse_json_or_ereport(). If the new interface is
used, an error can be thrown by passing the return value of
pg_parse_json() to json_ereport_error().

pg_parse_json() can still elog() in can't-happen cases, but it
seems like that issue is best handled separately.

Adjust json_lex() and json_count_array_elements() to return an
error code, too.

This is all in preparation for making the backend's json parser
available to frontend code.

Reviewed and/or tested by Mark Dilger and Andrew Dunstan.

Discussion: http://postgr.es/m/CA+TgmoYfOXhd27MUDGioVh6QtpD0C1K-f6ObSA10AWiHBAL5bA@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/1f3a021730be98b880d94cabbe21de7e4d8136f5

Modified Files
--------------
src/backend/utils/adt/json.c      |   9 +-
src/backend/utils/adt/jsonapi.c   | 537 +++++++++++++++++++-------------------
src/backend/utils/adt/jsonb.c     |   4 +-
src/backend/utils/adt/jsonfuncs.c |  29 +-
src/include/utils/jsonapi.h       |  46 +++-
5 files changed, 342 insertions(+), 283 deletions(-)