[Java] Apply new hash map in DictionaryEncoder

[asfimport]

Follow-up of ARROW-5814.

Apply new hash map in DictionaryEncoder to make it work.

Reporter: Ji Liu / @tianchen92
Assignee: Ji Liu / @tianchen92

Related issues:

• [Java] Implement a <Object, int> HashMap for DictionaryEncoder (is a child of)

PRs and other links:

• GitHub Pull Request #4786

_{Note: This issue was originally created as ARROW-5834. Please see the migration documentation for further details.}

[asfimport]

Micah Kornfield / @emkornfield:
Issue resolved by pull request 4786
#4786