DRILL-7086: Output schema for row set mechanism
Enhances the row set mechanism to take an "output schema" that describes the vectors to
create. The "input schema" describes the type that the reader would like to write. A
conversion mechanism inserts a conversion shim to convert from the input to output type.
Provides a set of implicit type conversions, including string-to-date/time conversions
which use the new format property stored in column metadata. Includes unit tests for
the new functionality.
closes #1690
