Also prettify variables json when clicking prettify query button

[bertyhell]

Is your proposal related to a problem?

When i click the prettify button in the web console only the query is prettified, and not the json for the variables.

Describe the solution you'd like

Both the query and the variable json should get prettified

Describe alternatives you've considered

You could have the user manually prettify the variable json or copy it out into an external json prettify tool. But that is less convenient

[rikinsk]

Fixed via #9969