pgsql: Refactor jsonpath's compareDatetime()

Refactor jsonpath's compareDatetime()

This commit refactors come ridiculous coding in compareDatetime(). Also, it
provides correct cross-datatype comparison even when one of values overflows
during cast. That eliminates dilemma on whether we should suppress overflow
errors during cast.

Reported-by: Tom Lane
Discussion: https://postgr.es/m/32308.1569455803%40sss.pgh.pa.us
Discussion: https://postgr.es/m/a5629d0c-8162-7559-16aa-0c8390d6ba5f%40postgrespro.ru
Author: Nikita Glukhov, Alexander Korotkov

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/52ad1e659967896ed153185328ffe806d69abcb6

Modified Files
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src/backend/utils/adt/date.c | 40 ++--
src/backend/utils/adt/jsonpath_exec.c | 262 +++++++++++++++++----------
src/backend/utils/adt/timestamp.c | 31 ++--
src/include/utils/date.h | 4 +-
src/include/utils/timestamp.h | 4 +-
src/test/regress/expected/jsonb_jsonpath.out | 37 ++--
src/test/regress/sql/jsonb_jsonpath.sql | 3 +
7 files changed, 237 insertions(+), 144 deletions(-)