Implement new Json parser reporting source locations.
Update JsonBuilder to use new json parser.

The new json parser reports accurate source locations.
Address code review feedback.
Abide to the 80-column limit.
Rename "utils.dart" to "json_utils.dart".
Address code review feedback.
Address code review feedback.
Fix test.
Fix identation.
Merge pull request #3170 from rpaquay/json-parser

Add json parser reporting accurate source locations.