Make Row type comparable

This PR addresses #1957 to make ``row`` type comparable and implements the ``EQUAL`` and ``NOT_EQUAL`` operators for the ``row`` type.
Couple more tests to add:
1) test with TimestampWithTimeZone
2) test with a row nested in a row
3) test with a row that has a non-comparable type in it (this should fail to analyze, since the operator won't exist)