[SPARK-4573] [SQL] Add SettableStructObjectInspector support in "wrap" function

Hive UDAF may create an customized object constructed by SettableStructObjectInspector, this is critical when integrate Hive UDAF with the refactor-ed UDAF interface.

Performance issue in `wrap/unwrap` since more match cases added, will do it in another PR.
A general comment about this test suite: would be better to use `===` rather than `==` in assertions to enable more friendly error messages with actual data values when tests fail.