DRILL-5517: Size-aware set methods in value vectors
Please see DRILL-5517 for an explanation.
Also includes a workaround for DRILL-5529.
Implements a setEmpties method for repeated and non-nullable
variable-width types in support of the revised column accessors.
Unit test included. Without the setEmpties call, the tests fail with
vector corruption. With the call, things work properly.
closes #840
