Re: remaining sql/json patches

based on this query:
begin;
SET LOCAL TIME ZONE 10.5;
with cte(s) as (select jsonb '"2023-08-15 12:34:56 +05:30"')
select JSON_QUERY(s, '$.timestamp_tz()')::text,'+10.5'::text,
'timestamp_tz'::text from cte
union all
select JSON_QUERY(s, '$.time()')::text,'+10.5'::text, 'time'::text from cte
union all
select JSON_QUERY(s, '$.timestamp()')::text,'+10.5'::text,
'timestamp'::text from cte
union all
select JSON_QUERY(s, '$.date()')::text,'+10.5'::text, 'date'::text from cte
union all
select JSON_QUERY(s, '$.time_tz()')::text,'+10.5'::text,
'time_tz'::text from cte;

SET LOCAL TIME ZONE -8;
with cte(s) as (select jsonb '"2023-08-15 12:34:56 +05:30"')
select JSON_QUERY(s, '$.timestamp_tz()')::text,'+10.5'::text,
'timestamp_tz'::text from cte
union all
select JSON_QUERY(s, '$.time()')::text,'+10.5'::text, 'time'::text from cte
union all
select JSON_QUERY(s, '$.timestamp()')::text,'+10.5'::text,
'timestamp'::text from cte
union all
select JSON_QUERY(s, '$.date()')::text,'+10.5'::text, 'date'::text from cte
union all
select JSON_QUERY(s, '$.time_tz()')::text,'+10.5'::text,
'time_tz'::text from cte;
commit;

I made some changes on jspIsMutableWalker.
various new jsonpath methods added:
https://git.postgresql.org/cgit/postgresql.git/commit/?id=66ea94e8e606529bb334515f388c62314956739e
so we need to change jspIsMutableWalker accordingly.

based on v39.