Paragraphs Preview for Gridstack widget

Problem/Motivation

It would be great to preview paragraphs in the gridstack widget.

Proposed resolution

1) Investigate how to preview paragraphs, and check examples and plugins in the paragraphs module.
2) Do we need and how we can pass paragraph render arrays into JS?
3) We will need to update GridstackBehaviour::view() and paragraphs-gridstack.js code.

Remaining tasks

@todo