pgsql: Fix errors in copyfuncs/equalfuncs support for JSON node types.

Fix errors in copyfuncs/equalfuncs support for JSON node types.

Noted while comparing existing code to the output of the proposed
patch to automate creation of these functions.  Some of the changes
are just cosmetic, but others represent real bugs.  I've not
attempted to analyze the user-visible impact.

Back-patch to v15 where this code came in.

Discussion: https://postgr.es/m/1794155.1656984188@sss.pgh.pa.us

Branch
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REL_15_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/90d6c65a2c2358bd80103afc0686c90c70d5417b

Modified Files
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src/backend/nodes/copyfuncs.c  | 11 ++++++-----
src/backend/nodes/equalfuncs.c | 25 ++++++++++++++++++++++---
2 files changed, 28 insertions(+), 8 deletions(-)