arrow

ARROW-11173: [Java] Add map type in complex reader / writer

This pull request adds support for Map types in FieldReader and FieldWriter.

Initial unit tests show how to add the following nested types:
- A list of maps: `List<Map<Integer, Long>>`
- Nesting a map as the value of another map: `Map<Long, Map<Long, Long>>`
- Nesting maps as both the key and value of another map: `Map<Map<Integer, Integer>, Map<Long, Long>>`

Appreciate any feedback or suggestions for improvement.

Closes #9151 from nbruno/ARROW-11173

Authored-by: Nick Bruno <nbruno@users.noreply.github.com>
Signed-off-by: Micah Kornfield <emkornfield@gmail.com>