[JS] Programmatically created dictionary vectors don't get dictionary IDs

[asfimport]

This seems to be the cause of the test failures in #2322

Modifying getSingleRecordBatchTable to generate its vectors programmatically (rather than deserializing hard-coded JSON), causes the new round-trip tests added in #2638 to fail. The root cause seems to be that an ID is never allocated for the generated dictionary.

Reporter: Brian Hulette / @TheNeuralBit
Assignee: Brian Hulette / @TheNeuralBit

PRs and other links:

• GitHub Pull Request #2726

_{Note: This issue was originally created as ARROW-3425. Please see the migration documentation for further details.}

[asfimport]

Wes McKinney / @wesm:
Issue resolved by pull request 2726
#2726