src: move JSONWriter into its own file

The JSONWriter feature is not inherently related to the report
feature in any way.

As a drive-by fix, remove a number of unused header includes.

PR-URL: https://github.com/nodejs/node/pull/32552


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Gus Caplan <me@gus.host>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>