Major Description
Currently the TimestampNTZ literals shows only long value instead of timestamp string in its SQL string and toString result.
Before changes (with default timestamp type as TIMESTAMP_NTZ)
```
– !query
select timestamp '2019-01-01\t'
– !query schema
struct<1546300800000000:timestamp_ntz>
```
After changes:
– !query
select timestamp '2019-01-01\t'
– !query schema
struct<TIMESTAMP_NTZ '2019-01-01 00:00:00':timestamp_ntz>
