Instead of relying on `serde_json::Value`.
BREAKING CHANGE: There is no longer `impl Typed for serde_json::Value`,
either parse directly into jrsonnet-evaluator, or use `serde_transcode`
It had no practical use, because it was not comment-preserving
There is in-progress version based on rowan parser, however it shares
no code with current implementation
BREAKING CHANGE: It is no longer possible to build jrsonnet-fmt