Modify the JsonLint library to return `array` instead of `stdClass`.

Summary:
Summary :Ref T5297. Make `PhutilJSONParser::parse($json)` roughly approximate to `json_decode($json, true)`. Generally when we parse JSON, we want the result to be an `arrray`, not a `stdClass` object.

Depends on D9622.

Test Plan: Wrote a few additional test cases.

Reviewers: #blessed_reviewers, epriestley

Reviewed By: #blessed_reviewers, epriestley

Subscribers: epriestley, Korvin

Maniphest Tasks: T5297

Differential Revision: https://secure.phabricator.com/D9623