add hasSelectionHandle: true to toWidget options

Problem/Motivation

I would like to have the drag handle attached to embeddable content blocks

Of course - the embeddable IS draggable, this is a UI element that makes it easier/more obvious.

Thank you for this module!

Steps to reproduce

Currently editing an embeddable does not show the drag handle.

Proposed resolution

Naive patch attached with the toWidget option hasSelectionHandle set to true

Remaining tasks

I can make a real patch if needed!

User interface changes

Adds a drag handle to the top of an embeddable content block

API changes

n/a

Data model changes

n/a