pgsql: SQL/JSON: Improve error-handling of JsonBehavior expressions

SQL/JSON: Improve error-handling of JsonBehavior expressions

Instead of returning a NULL when the JsonBehavior expression value
could not be coerced to the RETURNING type, throw the error message
informing the user that it is the JsonBehavior expression that caused
the error with the actual coercion error message shown in its DETAIL
line.

Discussion: https://postgr.es/m/CACJufxEo4sUjKCYtda0_qt9tazqqKPmF1cqhW9KBOUeJFqQd2g@mail.gmail.com
Backpatch-through: 17

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/231b7d670b218d6a5cde0574cf160c8157ab91fb

Modified Files
--------------
src/backend/executor/execExprInterp.c            | 78 +++++++++++++++++++++---
src/test/regress/expected/sqljson_jsontable.out  |  7 +--
src/test/regress/expected/sqljson_queryfuncs.out | 21 ++-----
3 files changed, 78 insertions(+), 28 deletions(-)