[Java] Support Dictionary Encoding for binary type

[asfimport]

Now is not implemented because byte array is not supported to be HashMap key.

One possible way is that wrap them with something to implement equals and hashcode.

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

PRs and other links:

• GitHub Pull Request #4792

_{Note: This issue was originally created as ARROW-5835. Please see the migration documentation for further details.}

[asfimport]

Micah Kornfield / @emkornfield:
Issue resolved by pull request 4792
#4792