[SPARK-3988][SQL] add public API for date type

Add json and python api for date type.
By using Pickle, `java.sql.Date` was serialized as calendar, and recognized in python as `datetime.datetime`. 
Could you add more formats support for Date? At least ISO8601, see some discussion here: http://stackoverflow.com/questions/10286204/the-right-json-date-format

We would like have jsonRDD() as robust as possible.