DPL: unify JSON representation of arrays in Variant

[aalkin]

@jgrosseo this adds an extra "values" layer in JSON representation of 1d and 2d arrays, consistent with labeled arrays.

[jgrosseo]

@TimoWilken @ktf @davidrohr Do we know what is going on with the CI? The failures here some to be unrelated (and there are other PRs where everything is red as well)...

[davidrohr]

@jgrosseo : At the moment they are all almost always failing. I'd try not to force-merge too much, since that would be basically untested (the fact that it fails for an unrelated reason does unfortunately not imply that it should succeed on a PR...).
@TimoWilken is working on the issue with macOS and o2, which seem to be related. I am not sure if that will also fix the full CI. I believe the full CI problem appeared after the websocket commit in DPL. @ktf has claimed to fix it yesterday evening. I am currently checking his fix in my full-system test. But the full CI is still failing. So either this is yet another unrelated issue, or the websocket fix is still insufficient...