[SPARK-12287][SQL] Support UnsafeRow in MapPartitions/MapGroups/CoGroup

Support Unsafe Row in MapPartitions/MapGroups/CoGroup.

Added a test case for MapPartitions. Since MapGroups and CoGroup are built on AppendColumns, all the related dataset test cases already can verify the correctness when MapGroups and CoGroup processing unsafe rows.

davies cloud-fan Not sure if my understanding is right, please correct me. Thank you!

Author: gatorsmile <gatorsmile@gmail.com>

Closes #10398 from gatorsmile/unsafeRowMapGroup.