[C++] Implement Fixed Size List type

[asfimport]

At the moment, we only support lists with a variable size per entry. In some cases, each entry of a list column will have the same number of elements. In this case, we can use a more effective data structure as well as do certain optimisations on the operations of this type. To implement this type:

• Describe the memory structure of it in Layout.md
• Add the type to the enums in the C++ code
• Add FixedSizeListArray, FixedSizeListType and FixedSizeListBuilder classes to the C++ library

Reporter: Wes McKinney / @wesm
Assignee: Ben Kietzman / @bkietz

Related issues:

• Integration tests for Fixed Size List type (blocks)
• [C++] ListArray comparison is incorrect (supercedes)

PRs and other links:

• GitHub Pull Request #4278

_{Note: This issue was originally created as ARROW-1280. Please see the migration documentation for further details.}

[asfimport]

Brian Hulette / @TheNeuralBit:
@xhochy do you think this would qualify for the "beginner" label and get tackled at a hackathon? I would like to see support for FixedSizeList in Python/C++ and I wouldn't think it'd be too hard to adapt the List type

[asfimport]

Uwe Korn / @xhochy:
@TheNeuralBit yes this surely does. It probably involves amending the Layout.md and implementing a first variant in C++ with the respective unit tests.

[asfimport]

Antoine Pitrou / @pitrou:
Issue resolved by pull request 4278
#4278