[SQL] Convert arguments to Scala UDFs

Author: Michael Armbrust <michael@databricks.com>

Closes #3077 from marmbrus/udfsWithUdts and squashes the following commits:

34b5f27 [Michael Armbrust] style
504adef [Michael Armbrust] Convert arguments to Scala UDFs

(cherry picked from commit 15b58a2234ab7ba30c9c0cbb536177a3c725e350)
Signed-off-by: Michael Armbrust <michael@databricks.com>