[report] Refactor JsonCostsPrinter module
[report] Refactor JsonCostsPrinter module

Summary:
In the following diff, we will add `JsonConfigImpactPrinter` that will share some common code base
with `JsonCostsPrinter`.  This diff prepares the sharing.

Reviewed By: jvillard

Differential Revision: D26665070

fbshipit-source-id: 5032e0611

jvillard/infer,facebook/infer,facebook/infer,facebook/infer,jvillard/infer,jvillard/infer,facebook/infer,jvillard/infer,jvillard/infer,facebook/infer,facebook/infer,facebook/infer,jvillard/infer,jvillard/infer