Raw JSON Writer

[tustvold]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.

Following #3479 we no longer use serde_json to decode JSON, this is not only significantly faster but gives us more control.

I would like to propose doing something similar for the write path, this would not only significantly improve performance but also give us more control over how data is encoded - #5197 (comment)

Describe the solution you'd like

I would like to deprecate the current serde_json based encoding mechanism, and introduce a new encoder that writes directly to a std::fmt::Write. Unfortunately the serde_json nature leaks out in a couple of places, so we will need to have a gradual deprecation of this functionality much like we did for #3479.

Describe alternatives you've considered

Additional context

[tustvold]

label_issue.py automatically added labels {'arrow'} from #5197