Add support for DICTIONARY encoding to PrestoSerializer (facebookincu…

…bator#6686)

Summary:
Extend PrestoSerializer to support deserializing dictionary-encoded data.

The format of dictionary-encoded columns is:
- 4 bytes: number of rows
- N bytes: dictionary column
- 4*numRows bytes: indices
- 24 bytes: 'instance id' (used by Presto, but not present in Velox)

Part of facebookincubator#6595

Pull Request resolved: facebookincubator#6686

Reviewed By: pedroerp

Differential Revision: D49532000

Pulled By: mbasmanova

fbshipit-source-id: 8f3adb3c9e61d842b1bc00ecced9f972892952a6