[Integration][JS] Integration Tests for Map Type

[asfimport]

ARROW-1279 enabled integration tests for MapType between Java and C++, but JavaScript had to be disabled for the map case due to an error. Once this is fixed, generate_map_case could be moved under generate_nested_case with the other nested types.

Reporter: Bryan Cutler / @BryanCutler
Assignee: Paul Taylor / @trxcllnt

Related issues:

• Completing integration tests for major implemented data types (is a parent of)
• [JS] enable integration tests for MapVector (is duplicated by)

PRs and other links:

• GitHub Pull Request #5371

_{Note: This issue was originally created as ARROW-5762. Please see the migration documentation for further details.}

[asfimport]

Paul Taylor / @trxcllnt:
After reviewing the C++, the JS version of the Map type is not the same (it's essentially a Struct except instead of accessing child fields by field index, they're accessed by name). We should absolutely update the JS Map implementation before the 1.0 release.

[asfimport]

Wes McKinney / @wesm:
Issue resolved by pull request 5371
#5371