[Java] ArrowFlightJdbcTimeStampVectorAccessor:getTimestamp returns timestamp that is supposed to be in UTC time but the timezone of the timestamp object is the local timezone

### Describe the bug, including details regarding any error messages, version, and platform.

When calling the getTimestamp method from the ArrowFlightJdbcTimeStampVectorAccessor class, the timezone of the Timestamp object returned is incorrect. The timestamp itself appears to be in GMT/UTC time but the timezone field of the Timestamp object is populated with the timezone of the JDBC client instead.

**Example**

timestamp on db: 2021-03-28T00:15:00.000 (UTC)

timezone of JDBC client: PST/PDT (Vancouver Time)
Calendar cal <- Calendar with UTC timezone
calling getTimestamp(cal) on a result set will return a timestamp like this: 2021-03-28T00:15:00.000 (PST/PDT)
where 2021-03-28T00:15:00.000 appears to be in UTC time but the timezone of the object itself is PST/PDT

### Component(s)

Java