This PR change to convert julian day to unix timestamp directly (without Calendar and Timestamp).

cc adrian-wang rxin

Author: Davies Liu <davies@databricks.com>

Closes #6759 from davies/improve_ts and squashes the following commits:

849e301 [Davies Liu] Merge branch 'master' of github.com:apache/spark into improve_ts
b0e4cad [Davies Liu] Merge branch 'master' of github.com:apache/spark into improve_ts
8e2d56f [Davies Liu] address comments
634b9f5 [Davies Liu] fix mima
4891efb [Davies Liu] address comment
bfc437c [Davies Liu] fix build
ae5979c [Davies Liu] Merge branch 'master' of github.com:apache/spark into improve_ts
602b969 [Davies Liu] remove jodd
2f2e48c [Davies Liu] fix test
8ace611 [Davies Liu] fix mima
212143b [Davies Liu] fix mina
c834108 [Davies Liu] Merge branch 'master' of github.com:apache/spark into improve_ts
a3171b8 [Davies Liu] Merge branch 'master' of github.com:apache/spark into improve_ts
5233974 [Davies Liu] fix scala style
361fd62 [Davies Liu] address comments
ea196d4 [Davies Liu] improve timestamp from parquet