pgsql: Fix string comparison in jsonpath

Fix string comparison in jsonpath

Take into account pg_server_to_any() may return input string "as is".

Reported-by: Andrew Dunstan, Thomas Munro
Discussion: https://postgr.es/m/0ed83a33-d900-466a-880a-70ef456c721f%402ndQuadrant.com
Author: Alexander Korotkov, Thomas Munro
Backpatch-through: 12

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/251c8e39bc6b0a3ff1620d9ac10888a7660e6b88

Modified Files
--------------
src/backend/utils/adt/jsonpath_exec.c | 37 +++++++++++++++++++++++++++--------
1 file changed, 29 insertions(+), 8 deletions(-)