pgsql: Support json_errdetail in FRONTEND code

Support json_errdetail in FRONTEND code

Allocate memory for the error message inside memory owned by the
JsonLexContext and move responsibility away from the caller for
freeing it.  This means that we can partially revert b44669b2ca
as this is now safe to use in FRONTEND code.  The motivation for
this comes from the OAuth and incremental JSON patchsets but it
also adds value on its own.

Author: Jacob Champion <jacob.champion@enterprisedb.com>
Reviewed-by: Michael Paquier <michael@paquier.xyz>
Discussion: https://postgr.es/m/CAOYmi+mWdTd6ujtyF7MsvXvk7ToLRVG_tYAcaGbQLvf=N4KrQw@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/d6607016c738a5ccdd9422f3c11778903a03cdbb

Modified Files
--------------
src/bin/pg_verifybackup/t/005_bad_manifest.pl |   3 +-
src/common/jsonapi.c                          | 121 +++++++++++++++-----------
src/common/parse_manifest.c                   |   2 +-
src/include/common/jsonapi.h                  |   1 +
4 files changed, 73 insertions(+), 54 deletions(-)