Make top level rows non-collapsible

[marcelltoth]

Summary

This looks weird:

We understand the incentive behind not allocating another level of nesting (left-padding) for the top level rows. The conclusion was to further align JSV with the product designs, and make top level rows non-collapsible.

This way we could have the label of the top-level rows start at exactly at the top left of the component, adding the notion of nesting visually, yet keeping the position of the children unchanged.

[marcelltoth]

Closing in favor of stoplightio/elements#1030