[SPARK-15648][SQL] Add teradataDialect for JDBC connection to Teradata

The contribution is my original work and I license the work to the project under the project’s open source license.

Note: the Teradata JDBC connector limits the row size to 64K. The default string datatype equivalent I used is a 255 character/byte length varchar. This effectively limits the max number of string columns to 250 when using the Teradata jdbc connector.

## What changes were proposed in this pull request?

Added a teradataDialect for JDBC connection to Teradata. The Teradata dialect uses VARCHAR(255) in place of TEXT for string datatypes, and CHAR(1) in place of BIT(1) for boolean datatypes.

## How was this patch tested?

I added two unit tests to double check that the types get set correctly for a teradata jdbc url. I also ran a couple manual tests to make sure the jdbc connector worked with teradata and to make sure that an error was thrown if a row could potentially exceed 64K (this error comes from the teradata jdbc connector, not from the spark code). I did not check how string columns longer than 255 characters are handled.

Author: Kirby Linvill <kirby.linvill@teradata.com>
Author: klinvill <kjlinvill@gmail.com>

Closes #16746 from klinvill/master.