QuerySelectorAll-770156: Refactor JSON cmd output

The command is now processing the node list into a plain object
so it can potentially be serialized if needed.
Also, the command does the util.findCssSelector bit as the converter
doesn't get nodes anymore but just objects.
This allowed to clean up the converter a bit (util and context are not
needed anymore in the data object).
Also, the context.exec was changed to avoid using the deprecated `typed`
Finally the node onclick logic was changed to rely only on one onclick function.
The required selector being passed as a data-attribute of the clicked node.

Signed-off-by: Patrick Brosset <patrickbrosset@gmail.com>