* json custom serialization; application for strtabs
* serialize using nesting
* make toJson more feature complete
* add since
* Revert "Improve JSON serialisation of strtabs (#14549)"
This reverts commit 7cb4ef26ad.
* better approach via mixin
* toJson, jsonTo
* fix test
* address comments
* move to jsonutils
* doc
* cleanups
* also test for js
* also test for vm