pgsql: Move some code from jsonapi.c to jsonfuncs.c.

Move some code from jsonapi.c to jsonfuncs.c.

Specifically, move those functions that depend on ereport()
from jsonapi.c to jsonfuncs.c, in preparation for allowing
jsonapi.c to be used from frontend code.

A few cases where elog(ERROR, ...) is used for can't-happen
conditions are left alone; we can handle those in some other
way in frontend code.

Reviewed 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/73ce2a03f30b52d6bfb26bc28f1e3e1aa1637577

Modified Files
--------------
src/backend/utils/adt/json.c | 2 +-
src/backend/utils/adt/jsonapi.c | 127 +-------------------------------------
src/backend/utils/adt/jsonb.c | 2 +-
src/backend/utils/adt/jsonfuncs.c | 126 +++++++++++++++++++++++++++++++++++++
src/include/utils/jsonapi.h | 15 +----
src/include/utils/jsonfuncs.h | 9 +++
6 files changed, 140 insertions(+), 141 deletions(-)