Uses protobuf JSON util instead.
packager/base/json_writer comes from Chromium base. We are going to
replace it with abseil, which does not have a JSON library.
The code is much more cleaner now.
This is unfortunately, at the expense of increased output binary size.
packager binary increases by another 100KB.
Change-Id: I83a9217a484cad3c41147ad9a75311384347c49c