https://issues.apache.org/jira/browse/ARROW-4142

This adds support for reading JDBC arrays and converting them to Arrow ListVectors.  JDBC does not provide a great way to get the array type; there is a ResultSet object for walking the array, but its ResultSetMetaData may not contain the right value type (H2, for example, returns a JDBC type of NULL).

This is based on apache#3134, which includes ARROW-3965 and ARROW-3966.

I found Arrow arrays to be very confusing, and I am not sure if I am using them correctly here.  One thing I noticed was if I added a null array to a ListVector of VarCharVectors, the next value in the VarCharVector would be empty.  I would appreciate any help on why!  The ListVector unit tests weren't very helpful.

For all other cases, this code seems to work.  I look forward to your review!

Author: Mike Pigott <mpigott@gmail.com>

Closes apache#3294 from mikepigott/jdbc-array-field and squashes the following commits:

66376dd <Mike Pigott> Support for reading Array records to ListVector from JDBC